Cyl sidewall wear with a 416

Hmm, could be the machine shop who did the bore went a little too much??
Also when putting more stroke in the engine the rod/stroke ratio is affected and sometimes this puts alot more pressure on the cylinder walls than if were stock. The rod is actually forcing the piston into the side of the cylinder causing the early wear. Replacing stock length rods with longer rods help but then you have to go with custom pistons with a different pin heighth to move the pin closer to the top of the piston.
I've heard that if you have bored the block out quite a bit and put a stroker crank in you can actually push the piston right through the side of the cylinder, prob at high rpms though.