Hey Vic welcome to the Stovebolt. I saw that truck on craigslist and was sure tempted to go after it. Great catch!
GMC sixes have the engine size as the first three digits of the serial number. You'll find the serial number on a small pad just behind the distributor. On a COE you'll open the floor covers just to see it.
If you check
www.OldGMCTrucks.com there is information to decode the serial number on GMC trucks. If you join up other there you'll find a thread discussing your truck.
However a serial starting A248 does not match the chassis designations and is probably a motor number. If that is the case, ignore the A and your motor is, or was a 248. I'm not sure what the A means, though I have one with that too.
You really need the serial number from the chassis plate, probably inside the drivers door, to determine what model truck it is. My guess is that will start F35 or F4 something.
