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.