A 270 has a 3.781" bore, a 4" stroke, and a 7" long connecting rod. That converts to a 96MM bore size. There are a lot of 96MM and 96.5MM Japanese Diesel pistons available on Ebay that have a pretty close compression height to a 270, and a piston crown about 1/2" thick that can be trimmed down to the same deck height as the GMC piston. For the dome piston head, just contour whatever part of the piston sticks out of the top to clear the combustion chamber shape. There's also an H beam big block Chevy connecting rod available that's 7.1" long, with a 2.100" rod journal size, which can be used with an altered stroke crankshaft- - - - -about 1/8" extra stroke is available that way. All these parts cost less than the scarce (and ESSSSSPENSIVE) GMC stuff, since they're 20-30 years newer production. There's also a 96MM slip-fit flanged sleeve available for that Nissan piston that can be installed in the GMC block so the engine can be rebuilt repeatedly without ever reboring it again. The cylinder head holds the sleeve down into a counterbore in the top of the block like a Cummins 855 engine or a Detroit Diesel. A "stock" engine is just a blank canvas to be used by a talented machinist to paint a masterpiece!
www.ebay.com/itm/195096233829?www.ebay.com/itm/184354665596?www.ebay.com/itm/403395951735? Check your private messages- - - -the flashing envelope icon at the top of each forum page.
Jerry
