I hear people talking about big block and small block 727's. I've purchased two 727'sto use on a couple of cars. The pan is the same on both but they different measurements on the maiting face at front. Are there numbers or codes I should look for on the block to decide which is which? The cars are a 40 Desoto and a 47 Desoto suburban by the way. Is there a way to post pictures on here, I will if it can be done and someone tells me how.