I have a BBC that is driving me crazy. The engine serial number says it's a '79 402 and in checking the head casting numbers they are for either a '72 402 or 454. I was told that the engine was a 454. In checking the back of the block there are 2 sets of figures. To one side there is ONV and a little ways away is GM10T. There are no other numbers I can find. The engine number is T0505TLM.

You need to get the casting number off the rear of the block, probably on the drivers side on the bell housing lip. It's a six or seven digit raised number with no letters.

Have you been to MORTEC's site? It will show you where to look and has some codes as well.

http://www.mortec.com/