Joe, while I agree that the 50 oz imbalance on the "5.0L" Mustang engines is not a good thing for higher RPM use, I would be very leery about trying to use a stock 5.0 block approaching anything near 600 HP, again, depending on the intended use. Several years ago, a buddy made me a deal I could not refuse, for his old 331 cube SB Ford engine. It had a stock 5.0 (hyd. roller) block, an offshore 3.25" stroker kit with flat top pistons, a moderate solid flat tappet cam, out of the box AFR 185 heads, and a Holley 650 on a Victor Jr. intake. On a buddys engine dyno, it made 485 HP, and in my 3050 lb 85 Mustang Stocker platform, ran a best of 10.28 @128 MPH, using my 4 speed Jerico, shifting at 6800 RPM, hitting 7200 thru the finish line. It ran perfectly for a couple of years, and at the end of 2015, I decided to freshen it up. Good thing! Upon teardown, #1 main bearing cap came split thru the middle, and noticeable cracks were found at the main bearing webbing. Granted, my 331 has a 28 oz imbalance, rather than the more desirable internal balance, so maybe with a zero balance the block would have fared better. However, after looking at another 5.0 block I had laying around, I decided to use an earlier (1974) 302 block a buddy had laying around. I don`t know how much (if any) stronger the 74 block is, but unlike the 5.0 block, at least the main bearing bolt holes and head bolt holes SEEM better, in that they are blind. In addition, my machinest buddy installed a main cap girdle, which will hopefully help a bit. I would have much prefered something like a Dart or World block, I would rather have put that money towards FE stuff! Again, on a street type application, with occasional WOT blasts, the 5.0 block would have been fine, but I tend to lean on my stuff a bit more than that.
