[FFR428]

I think it will go 4.13 no problem. 4.23 might be a stretch but do the drill bit test between the cyl walls through the freeze plug holes. A 17/64" bit will fit between a 390 wall casting a 13/64 between a 428/406 casting and 8/64" and 5/64" for the 427's. You can convert the sizes as needed. The 64" are just a universal standard given. This is a fairly quick and accurate way to tell the wall thickness as far as casting. That 390 might fit the 428 13/64" bit wall thickness and would prove good to 4.13+. A sonic of course the best way but this is just a quick field helper. Use the shank of the bit to gauge between the cyls. Some guy's use the allen wrench test to the same effect but I feel the round bit shanks are more accurate. See what you can find. G.