You need to check the cyl wall core thickness to see if it's possible. The best way is to sonic map the block. But there is an easy field test you can try to see what wall cores were cast into the block. the test is called the "drill bit test". You need to knock out the blocks freeze plugs (three on each side) to access the cyl wall cores. You will then see the cyl wall cores and the gaps between them. Years of crap and crud can buildup so you need to scrape away some of that to get an accurate reading. If a 13/64" drill bit shank is a snug fit you have a very good chance of the 4.13 overbore and the block has 406/428 cyl wall cores. If a 17/64" drill bit shank fits snugly between the cyls the block has std 390 wall cores and will make the overbore to 4.13 impossible. As mentioned this is a basic field test and a sonic map will net the best results and to thickness and coreshift. even if the block has thicker wall cores coreshift can spoil the party. You can convert your bit sizes to suit your needs. The 64th's is just the standard measurement given for the test. Also credit is due to Dave Shoe on the net54 forum for inventing the drill bit test. It's a pretty neat way to check the blocks wall cores. Even if you can't acheive the 4.13 overbore you can indeed get a 3.98 428 crank and build a 410+. Stroker kits from Scat can even net you more cubes but you need to go to a 6.700 BBC rod.