340

I know a place that takes them 318’s to a 4 inch bore if they pass the sonic check.
I have read that it has been done before.
But until I measure it myself.......

Seriously, a .130 overbite? Maybe. Depends on the sleeve used.
I have personally laid my eyes on ONE 68 vintage 318 block that was bored to 4.040, it was a dirt track engine from many years ago