Piston deck height isn't the limiting factor on line boring (I've done dozens). It's the fit of the crankshaft and the cam. Stovebolts have a gear drive, so the teeth can bottom out as the crank is raised in the block. Chain drive engines like a Chevy V8 can get a sloppy chain fit and late cam timing after a line bore. There's actually an "engine rebuilder's" timing chain available for some engines that is a TINY bit shorter to compensate for a line bore. Raising the crank more than .002" during a line bore is considered to be a bad practice- - - -most of the machining is done to the main caps after shortening them about .010" in a milling machine.
Air cooled Volkswagen engines do have oversized OD main bearings available, since the two halves of the crankcase form the main bearing bores. I've installed over/under mains on a VW rebuild- - - -oversized bearing OD in a line bored case, with an undersized crankshaft.
Jerry
