Welcome to the board!
If the VIN in the door jamb & SPID label in the glove box match, the SPID will tell you what the truck had from the factory. Whether it still has those parts will take more digging. Here's an example of my Chevy Burb. Chevy & GMC VINs are very different though. W/BASE should be 115.0 for a SWB.
IF it's really a V8 the VIN should read something like, CE10D-?B#####
C = 2wd, K = 4wd
E = V8, S = I6, M = V6
1 = 1/2 ton
0D = 67-69 Fleetside, 0C = 67-69 Stepside
- = special for PA, MA, NY otherwise left as dash
? is assembly plant letter code
B is year code (C=67, B=68, A=69, Z=70, 1=71)
# is 5 digit serial number off the line
The 327 & Auto should show up on the SPID as a line item since they weren't standard equipment. Looks like 327 was an available option too. That should give you some stuff to look at. BTW, page 10 of LMCTruck.com web site will help you decode the VIN & a few other numbers.
Look on the back side of the rockers underneath for rust. Also look at the cab supports going to frame in same area. Inside kick panel where floor meets firewall just in front of the doors. All places rust might be hiding. Good thing is there are patch panels for "almost" anything you might need if you find something later too.
Good luck on the purchase.