The freeze was when we were in Seattle - it got down below 0 for several days and the power was out.  The more I think about it, I wonder if I had drained the block via the petcocks prior to all this because the area that I remember seeing the ice flow was behind the generator on the right side.  But like I said, there is no staining or any other visual indication of water coming out of the block.  You would think you'd see some staining.

Thanks to everyone for the insight and suggestions.  Never had the occasion to use Marvel and hadn't even heard of Seafoam.  As stated, the purpose of Marvel is to free up the rings - can I assume that the rings may stick to the pistons in a freely turning engine?  Just for my knowledge.
Great insight that the any damage will more readily show up when heated.  Skip a few steps that might not tell us much and get to the meat of the problem.  What is a good break in oil?  Valvoline 10/30?  Zinc additives were also mentioned.  When I fill with oil, I'll pour some over both rocker arms.  Also rotate the assembly with the valve covers off to check that none of the valves are stuck.
Probably should throw on a new filter while I'm at it.  Old canister type - Wix?  Doesn't Wix make NAPA filters?  Are they the same?
The car is still 6 volt.  The good news is that I can grab the battery out of the tractor for the short term.
Mike

We moved from Seattle in 2006 and are now about 2 hours north of Spokane almost to the Canadian border.  The good news is that I now have a wonderful, heated shop.  The bad news is that I'm 26 miles for the nearest parts store.
Thanks for your offer of a potential block if/when it gets down to that.  I'll keep it in mind.

already stated engine turns freely. mix some engine oil with 3parts gas 1 part oil, feed it into carb as trying to start,this ensures some lube to valves and rings instantly. have used this on several engines that sat for long period .bigest issue is sticking faves. fact we are looking for cracked block getting the engine to run is important to determine if in fact there is a crack. air pressure  not the best way, get it running and up to temp is 1st step

Outstanding idea by Kultulz remove all the plugs and put some lube into the cylinder Seafoam or Marvel oil put a good amount it to cover the top of the piston spraying it in give fairl good coverage let it sit a least overnight with the plugs in to get down well. REMOVE the plugs spin the engine to get the fluid out before attempting to start the car it should get a lil messy make sure as much liquid is out as possible just curious are you still running with 6 volts or did you convert to 12volts good luck again

When I do a compression check by spinning the engine with the starter, I assume I should try to get some oil pressure before starting.  It's been dry for almost 30 years.]

The hardest on an engine is a cold start, especially if it has not been turned for thirty years. You might want to consider using SEAFOAM in the cylinders to free the rings (let set for a few days with plugs installed and expel when turning the engine over with plugs removed). Also prime the oiling system, turn the engine over by hand a few times to distribute oil while priming. Reinstall plugs and then attempt fire. You will get a more precise compression reading on a warm engine.

Also, an internal coolant leak may occur on a cold engine, warm engine or combination.

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i would put the coolant back in,with some antifreeze,re connect the rad put the oil back,remove plugs and spin untill some oil pressure. plugs back in start the engine,if the block is cracked internal the oil will turn milky. as it warms up  external cracks  if they exist will leak. be sure to put the pressure cap on fully ,you want pressure in cooling. if water was left in the most vulernable aria is around the motor mount arias. don't worry about the sleve that repair if was inst buy a engine shop it is the last place i would worrey about.. air is misleading at this stage.. if water turns milky you have a internal leak re freezing. just pull the engine .how cold has it bin, a major freeze with small amounts of water left in will be hard to find if internal. you need a little luck ,but your issue is not rare hear I'm bc.

“The machine shop was in Seattle. IIRC we had to sleeve one cylinder. I'll have to dig around to see it I still have the paper work.”

If you’re still around Seattle, I’ve got a couple probably good blocks in storage if it doesn’t come out well.

They’re down in Tukwila.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

The head gasket is designed to be somewhat compressed I doubt if you will have any issues unless it has failed between the cooling jacket and the cylinder . If you have not pulled the valve covers off, I would and just pour some break in type oil or zinc additive down the push rod holes on to the cam to prevent any wear  while you spin the engine to do the compression test . The engine has been sitting a long time and maybe overkill but its only a few minutes work to protect the cam . Its is possible that some gaskets may be dry do to the age but I would not worry about them now , you need to find the source of the water as was said earlier the plugs on the engine that most people refer to as freeze out plugs are there for casting purposes some time you may get lucky and one pops but that was not its designed to do. If you drained the oil you need to put it back if you want to build oil pressure. Do the compression test with the throttle plate held open to get the best results If you have a low reading in two adjoining cylinders than most likely your head gasket has failed at that point . I think once you start looking around the problem will jump right out good luck keep us apprised 

Thanks for the insight.  The responses I'm getting are leading me in the right direction to figure out where I'm at.  Never done this kind of investigative mechanics before and don't know what to expect so I'm being very careful.
I got some PVC end caps today that should slip inside the radiator hoses to isolate the block.  I'll first pull the thermostat then apply air and see if anything different happens.  I'll pull the plugs to see if there is any evidence of water and listen to each cylinder while applying air.  I've drained the oil - so if anything gets into the bottom end, water should flow right out the drain hole.
When I do a compression check by spinning the engine with the starter, I assume I should try to get some oil pressure before starting.  It's been dry for almost 30 years.
Will gaskets degrade over time when not being used?  You mentioned a head gasket getting compressed which I assume will show up on a compression check.
I'll let you know what I find out tomorrow.
Thanks for all the input.