I have a 55 Merc with the tea pot and wanted the new 390 CFM Holley.  I did not want to buy a B manifold because I am still thinking about the Mummert manifold, even though I like a stock look.

I bought the 390 Holley and a Trans-Dapt carb adaptor (#2064) from Summit.  The adaptor comes with the holes cut in at the tea pot bolt pattern but the holes are not drilled all the way through.  I then purchase allen wrench driven bolts.  These were flat topped with a 45 degree angle from the edge of the head to the shaft.  I then had the machine shop drill the holes with the 45 degree taper so the head was slightly counter sunk and the angle of the bolt head matched the adaptor. 

The adaptor was then bolted to the manifold with the original spacer in place and the Holley was installed on the adapter.  The original throttle rod fit perfectly into a hole on the Holley but the clip that held it on the tea pot did not.  The machine shop drilled a small hole in this shaft for a cotter pin to secure it in the linkage of the carb.

My oil bath was dried out and dust and crumbles were falling out of it.  I reused the oil bath by using someone elses idea from this site.  I cut out the guts that are attached to the top lid of the oil bath, put the base of the oil bath on the carb,  then installed a 9" chrome air cleaner inside the base with a wingnut to secure, and finally put the lid over the after market air cleaner with its own nut.  It is a good paper element air cleaner inside but appears to be the stock oil bath on the engine.

I hope this gives somone some alternatives for a carb upgrade without a manifold change. The change to the new Holley is like night and day over the tea pot.  The adaptor costs about $20, bolts were $4, and the machine work cost $10.  The other adaptors I found on the internet were about $90-100.  At that price I would have bought the B manifold off of Ebay.

Congratulations on your most informative and successfull carb swap, this sort of simple and well detailed article by you is part of what this site is about, a job well done!

One suggestion on the intake - I have one of the early mummert intakes, and I just painted it engine color.  Nobody notices that it isnt stock.  Pretty funny, actually.  From looking at the website, his new one has the "Mummert" logo on it, so you would have that to contend with.  Ive been trying to figure out if there is a good way to remove that and blend it in with the rest of the casting so I could do the updated manifold and paint it similar to my current setup.

And Kevinwalshe, I may have a holley 390 that im going to put up on ebay or sell here soon, although honestly after running them back to back, I found the Holley 465 that is designed for these engines to make a little more power than the 390 without losing throttle response.  Just something to consider

The car drove great with the new distributor and the 390 carb out of the box.  So everyone here is right about the distributor change.

I just received the Pertronix 3 in the mail.  I am putting it on this weekend and will update with my opinion.