3 9/16" is a 235 bore size, but the 235 compression rings are only .093" wide (I just measured one). Try to find an industrial engine like a Hercules, etc. with a 3 1/2" bore that uses a 5/32" compression ring, get some .060" oversize rings, and make the GMC piston fit the wider ring.
That's assuming your 228 is standard bore, right?

EDIT:

A vendor on Ebay has spacers listed that will allow you to use 235 top rings with those pistons. They are flat steel shims that fit above the piston ring in an enlarged groove to make the top-to-bottom height of the ring groove correct. Drop me a PM and I'll forward the Ebay link, as the PC Patrol doesn't like them included in open forum posts.
Jerry



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