I'm waiting on delivery of a set of GMC 270 pistons and connecting rods from a recent Ebay purchase, just to get an extra set of connecting rods. I have no use for the pistons at the moment, since the engine I'm planning to build will have an altered stroke, and it will use flanged slip fit cylinder sleeves and pistons for a Japanese Diesel. They are the domed style. If they might be useful for your buildup, please PM me. Piston weight does not affect the crankshaft balance on inline six engines, since the 120 degree separation of the rod journals makes for an inherently balanced rotating assembly, assuming there's not a big difference in weight between cylinders.

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