It is a TDB suffix block so the engine id code is v0516TDB. However, it is a factory 4 bolt main, so it can't be a 307 or a 327. It is definitely not a dz motor. No dz anywhere on block. Therefore it has to be either a block cast in 68 or 78 with date code D208. Other puzzling thing to me is the engine serial/VIN #s C8Z192394. The "C" designation in the first position seems strange to me as well. I thought it was supposed to be a "1". Yes I know chevy used C to denote factory replacement blocks but the following numbers are not a GM block part number so it has to be the vehicle VIN sequential number. Would really like to find out whether it is a 1968 or 1978 cast block and maybe narrow down what vehicle model(s) it came from.