The advantage to boring the cylinders out as much as possible is you can then de shroud the valves. Concerning how much you can over bore, I would always have the shop doing the work sonic check the cylinder walls, that is the only way to know. I recently had a last year 1987 slant block safely over bored .080 and it could have gone bigger, but that worked with the pistons that I wanted to use. If you need an big bore slant head gasket AussieSpeed has those.
