If you want a complete identification from the gang, you'll need to get the casting codes and the date codes in addition to the serial numbers, etc. And keep in mind that the early 261's (out of the '54 mold) do not have Captain bars (or LT bars for you Navy guys).
Remember that both 235's and 261's out of the '54 molds (for the Advance Design trucks) were still being produced as crate/replacement engines for the earlier model trucks as late as 1959 and perhaps later. So it is possible to find an early 261 in a later model truck. My 261 is one of those engines (made in '59 out of the '54 mold). It was a direct bolt in upgrade to my '49 3800 -- no modifications required to engine mounts or water pump
