Isn't 370 the model number?
Of the "AD" style GMC trucks i've seen, the model number was on the side, about in the spot where the word Chevrolet would be on a chevy.
Of the "Task Force" style GMC trucks i've seen, the model number was tward the top center of the grill just below the GMC logo.
There's a guy near me with a GMC 350 "AD" style truck.. the truck just so happens to have a 350 V8 in it, and he tried to tell me that the 350 on the side indicated that it was the original motor.. but after asking around here, I learned that 350 is actually the model number.
That was a big truck.. if it's model number was 350, then 370 seems like a logical model number for a big GMC truck, too.
Way more likely than a straight 6 being a 370, anyway.
Altho I understand GMC had a series of oddball engines, like a V12 702 cid motor! There were also 305, 351, and 401 GMC V6 engines.. but not a 370 I6
