It's very obvious you've never been inside a GMC engine. It's already got full pressure oiling, a huge oil pump that flows far more oil than a stovebolt Chevy, full flow oil filter, and aluminum pistons- - - -they were all built that way. Is there some reason to believe the cylinders are worn enough to require another rebore job? Unless the cylinders are scored or have bad taper wear, there's no reason to whittle away more cylinder material- - - - -just do a slight scuff with a glaze breaker or a button hone to create the cross-hatch pattern needed to seat the new rings. If one or more cylinders are rust pitted or scored, install a sleeve and reuse the same pistons. Custom made GMC pistons are horrendously expensive, just because the people who make them are greedy and the people who purchase them are gullible enough to pay. I have a problem with Clifford's- - - - -their promises of major power gains with simple bolt-on items are blatantly false, and they refuse to publish any documentation of their claims. I have a problem trusting people who tell tall tales. The last GMC rebuild I was involved in was on a 256 cubic inch- - - -an oddball Canadian military engine that was a hybrid of a 248 and a 270, a 270 bore and a 248 stroke, IIRC. The biggest problem was finding the correct intake valves. I also straightened a twisted connecting rod and put a knurl on the piston skirts to get the clearance right after honing the cylinders. The rebuild turned out very well with using the original major parts such as pistons and connecting rods, and the crankshaft only needed polishing, not regrinding. GMC's are pretty tough engines, and they were made to be rebuilt multiple times. Good luck!
Jerry
