Motor isn't what I expected

[Alberta Newbie]

Hi everyone, can you help me out with ID-ing this motor? I've been trying to figure out the horsepower, and now I'm not even sure I know the size.

It's in a 1972 GMC 3/4 ton, which I was told was original and only had 45,000 miles on it. But now that I started looking I found a plate that says it was rebuilt.

Model XC120087
Serial X31791
Bore 040
M 01 T 01
Engine Rebuilders Ltd.

The VIN says TCE2421522076 and the SE (?) is FT0705638. The plate in the glove box just says 350 CID V8.

Any help greatly appreciated...