[Barry_R]

As referenced earlier, the 390 was a 4.050 bore and a 3.781 crank. The 428 was a 4.130 bore and a 3.984 crank. Ford 428s had a different water jacket core which can often be identified by the "428" cast in the bottom of the inner water jacket right under the center freeze plug.

I don't care what any ebay peddler says - the average 390 block cannot be bored out to a standard 428 bore with any guarantee of a long healthy life. Some of those guys are taking any $75 dollar core they can find and turning it into a $1000+ part with a boring bar and a "trust me" smile.

Likely that perhaps 10% or less of the 390 blocks out there are going to be ok at that bore. If you are fixated on going .080 over on a 390 you should invest in a sonic test before boring - and be prepared to discard several blocks. Or just go with a stroker package for cubes, make nice power, and leave the bore at a safe dimension without any risk or drama.