Pre-loading the motor mounts THAT much doesn't seem like a very good idea. I assume you are using the original cross member from the B20/M41 setup. If that's the case, I would be tempted to take the cross member to a wrecking yard (or maybe a Volvo specialty independent mechanic that might have a later 240 up on a rack) and compare the two. My gut tells me that when Volvo went to the B21/B23/B230 they were more likely to modify the cross member than the holes in the frame rails (which may have also been used as some sort of tooling mate holes during assembly = more costly to relocate). But I may be all wet. I'd still check it out before going hog wild with a rotory grinder. You're likely to run out of edge distance on the rear holes before you get everything to sit down in a "relaxed" position.

What about the front drive shaft length? Possibly one from a later year could be used there if needed?????

Good luck with the project!