Hi Betsy, Good news! although Mummerts site list that an ECZ block can be 292, I have dismantled about a half dozen ECZ blocks and all turned out 312's so chances are very high that you do have a 312!
The downfall is, parts are scarcer and more expensive for 312's and they are prone to cracking in the main web areas due to the larger mains. Read Mummerts Y block assembly errors page! May want to magnaflux in those areas.
The C heads are a great all around middle of the road head, however the G's, 113's, 471's and B9's have the larger intake valves.

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

Thanks Billy! Here is a few photos from last night!

http://forums.y-blocksforever.com/uploads/images/a42c4f6c-6325-4f20-873c-
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How about a picture of the crankshaft flywheel flange. Even if it is a 292 it can still be made into a great road worrier that will push you 54 down the road with ease.

Gary Ryan San Antonio.TX.

I will be taking that apart tonight, the pics I posted were the farthest I got. My day job has been keeping me away! I am pretty damn confident after all the other numbers I have found it's a 312...