I'm very intrested to know about the rocker arms you have in that head on the GX270. Are you sure it's a GX270? I can't recall seeing any GX270 with flattop piston unless you milled the piston and decked the block.
I'm working on a GX270 right now that has a billet long rod, billet short piston, billet lifters, 1.2 ratio roller rockers, billet cam, welded combustion chamber head, stainless stock size valves, ported and polished, and an ARC flywheel. This build has been a headache since trying to find the correct piston and long rod since there are none available for the GX270. Only the billet stock length rod.