swapping '79 Diffs into a '68 truck

[backwoodsK20]

I've got a 1968 Chev 3/4 ton, and I really wanted to put newer diffs in with different gearing and lockers. Mainly because I want disc brakes and something that's not geared to 4.56 so I can take it on the highway without holding the pedal to the boards. So I bought a '79 chevy 3/4 ton parts truck, it has 3.73's with Detroit lockers in it and plan to swap them over. Before I get into it, whats the easiest way to tackle this project? Will I be able to simply unbolt the diffs at the leaf spring mounts and swap over the diffs and springs at once? or are the mounts on the frame different, and am I better off just leaving my stock leafs on the '68 and swapping just the '79 diffs over? Are the newer style diffs slightly wider, will there be any modifications I should know about in advance, etc. Any help greatly appreciated!