while Chev trucks ran the 216, then the 235.and rarer 261 (it had exhaust valve rotators!) GMC had its own line of premier I6's. As noted, the 228/248 (changes in bore/270 (248 plus stroker crank) , and the 302, which while outwardly was identicle, had a slightly longer block. These Jimmy truck 6's are not to be confused with Chevys, which were just car engines. The GMC's had forged Al, expansion slotted pistons, stellite seats, i believe the rods were forged also. I got a Floyd Clymer "How to Hotrod Your Chevy ^ book, CR about 53. It has a chapter or 2 on the GMC's & some eye popping pictures. These beasts were so king hell for stout they were the choice of early Salt Lake guys & "pole racers"- guys who dragged from street pole to street pole. Being so more robust than the Chevy 6, they were cranking out 300 HP on alchol/benzin in the early 50's with STOCK crank, rods, & pistons (Venolia!) Man-A-Fre or was it Hildebrand- made Al direct port injector heads for them. Imagine finding one of THOSE at a swap meet! The stock carbs were elegant, tall Zenith 1bbls, with changeable venturis. You just had to go over the details of one to see that it was a real, long lived, king hell truck engine...only 4 mains, as was the practice. ...I mourn thier passing. (Plus, they looked good: the head, rocker box, & side cover had very pleasing lines....Mutt