Decoding my engine

[pcdave]

Hey guys, new to the forum. I picked up my 68 LWB C10 about 2 months ago...it was an older restoration, floorpans solid, rockers solid, just needed some general cleanup, some surface rust repair, and new bed floor.

Anyway, I am considering my powerplant options. The "350" that is in it runs ok, but it is a little tired and I have been looking at the 5.3L swaps. Before I run off and tackle that, I'd like to know what is in the truck...the previous owner said it was a 350, but he also had the timing set at 36+ degrees and the thing ran like hell until I stuck a light on it.

The casting number off the block is 3970010...which could be a 302/327/350, from my searches on the web. I checked the VIN on the truck, it was a factory 327 truck. If it miraculously is the original engine, I'd like to retain it (freshen it up) ... if not, then it doesnt much matter.

Can someone clue me in on how to verify the engine further, short of pulling it?

Thanks!