Cletis is right. GMC is has very little in common with a Chev engine. If you own a GMC, I would suggest buying a GMC service manual instead of trying to compare it to Chev. The GMC manual is pretty straight to the point on how they want the valves adjusted.

https://plus.google.com/u/0/1126369...0779876610&oid=112636930370126476644