BINGO. Thanks to you all, I found the block casting number right where you said it, "could," be: Right side, far forward, way down and under ledge below the, "GM," cast letters. Lots of wiggling under the truck this morning. Took your suggestion and used my digital camera. Tight spot, but it captured the number:
3733950, which under another chart in another site, corresponds to 1954 or 1955 production 261.
SO - with that, any last ideas on where/what this danged engine, "55xx," serial number comes from??? 1955?
Thanks again; you all made the difference and I hope the thread helps someone else too.
Dennis
