Steelonsteel,
Your engine casting number 3769925 indicates a 1960-62 Truck 261 (261 confirmed by the "Captains bars" on side of block behind where the starter mounts). The casting date code 7 11 5 I believe indicates "July 11th 1965". That should be accurate as that blank engine serial number surface being left unstamped indicates the engine is probably a later cast service replacement (others will chime in to clear that thought up).
The head casting number 3836850 indicates a 1956-62 Truck 261 (with the large temp sender hole).
The "split exhaust manifold" casting number 3836108 (seen in one of your attached pics) ID's that piece as a factory 1953-55 Corvette 235 exhaust manifold (see screenshot below from a known Corvette info site). It was commonly used to upgrade engine performance back in the day. That piece is quite a nice find as they are very sought after.
For a bit more info, check out this older thread
about this manifold.
All around a fantastic good find!
Dan
