I have used several the World aluminum blocks (HEMI and Wedge) and not had any unusual problems, no leaks, and just the usual machine work required (line hone, bore hone, vicious cleaning of left over shavings, deck checking, etc.) but all that is to be expected. I had one that had the rear main seal slightly off, but I found that during mock up and fixed it easily. Early blocks had cheap main studs but they're all ARP now. Smallest motor was 750 HP with >10000 miles on it and still running well, NA dragster was right at 1000 and a blown HEMI at 1600.

At the time KB blocks were running a year out, but Ken Black has got that back into line now. I'd go KB for the next one.