IMO, the 742 is the best case to have, simply because of the larger pinion shaft and the fact that the pinion depth is shimmable instead of the 489's crush sleeve set up. I always try to seek out a 742 case if possible, and every car I have has a 42 case in it. I do however have a couple 41 cases and they are just fine for everything but the high HP drivetrains.
FYI, I parted out a 68 Roadrunner, 383 4 speed car a couple years ago that came factory equipped with a 741, 3:23 open center section. Don't count out the 41 case, just build what you have.
If I was doing your swap, I would redo the housing and all of the components while it was still on the bench, but if you don't have your ideal center, just put the one you have in there for now to complete the swap. You can always find and rebuild your ideal center and swap it in while the rear is in the car!! I would stay away from the "Green" bearings if this is a street application, as the green set up has no side thrust load capabilities and will not handle much cornering, they are a race designed piece that is made for straight line performance. Good luck with the swap, Geof
