Yeah, those are the numbers I'm talking about. Those will tell you what the year the block is at least. As for the transmission, yeah, the Jetaway was used in the 98 for sure. The hydromatic was used in the base 88 in '56. It sounds like some things were switched around through the years. Maybe a '55 324 was swapped in to replace a blown '56, but the transmission was kept? It's hard to tell without knowing the block casting numbers.