Don't get caught up into the mentality of doing the swap because you think you're getting a stronger axle; you can do a lot of wheeling with the D25/27 and they are pretty much the same in strength as the D30. The main advantage to doing the D30 swap is to decrease turning radius with larger diameter tires. You can put discs on the D25/27 using full size Chevy 1/2 ton caliper brackets, calipers, hoses, and '77/'78 CJ 1-1/8" rotors. There are quite a few write ups on the net about it, including the 3b page and www.earlycj5.com
. You can also do Chevy brakes on the D30, or you can just find a D30 axle with discs already on it (I got one locally for $50 complete with hoses and tie rods). If you simply must swap it out, you want to get a '72-'79 CJ model as they are narrow trac and have the 6 bolt hubs. If you want a stronger axle, go with Wagoneer 44s or something of that nature.