I know the answer to this question... for the 2V blocks. Basically, there is no difference (same head bolt pattern), but there is some difference in the timing chain tensioners. I believe to put a 4V on a 2V block, or vice versa, you had to use half of the 2V tensioners and half of the 4 valves ones. Other than that, I think you used the front cover to match the heads and had to do some ECU magic.
Again, that's for the 2V-4V, so take it for what it's worth.
Dan