I have a 57 gmc that I am working on. just have the chassis on stands with the tci front end in. I have a 8.8 ford diff from an explorer with the discs etc. and a homemade 4 link from welders series. anyway, just a word of caution before you weld in your tci front end make sure to get the geometry right. they sent me the wrong crossmember so I put it all together and tacked it in, assembled it as a mock up and found it was way out of whack. after checking out a few sites, mostly heidts mustang II geometry, I ended up taking it all out and trial end errored it untill I got it right. with the lower control arms sitting level it is best if the upper control arms are actually sloped downward at the inside/frame end. like a couple of degrees. that way when you go over a bump the wheel doesn't tip out at the top and make your tires rub on the fenders. also you will need to build in some antidive, the upper "hats" are usually tipped up at the front about 4 degrees. you have to put the front end together and mock up the cab and fenders etc so you know what you have for space between the wheel mounting surface and the fender, and also the wheel mounting surface and the frame. one more thing, when you drop the truck, as in with mustang II and drop spindles, you will probably want to put the crossmember an inch ahead of the original centre line for the axle. otherwise the wheels look like they are too far back in the fender wells.
I have the mustang II tci with the 2 inch drop spindles and had to c notch the frame out back to get the stance I wanted-2 degrees of rake.assemble it all and use a digital level so you know what you have before it is too late, like after welding. otherwise you will be looking for a set of no drop mustang II spindles so you don't have to c notch. or, maybe that was your plan anyway. when I did mine I had the frame up on jack stands that were modified so there was a piece of threaded rod and a jam nut in place of the moveable jack stand part. this had a 3/8 bolt welded on the top that would go through a hole in the truck frame with a jam nut on top of that. I had one at each corner so I could move the threaded rod up or down and then lock it there, to get the frame perfectly level side to side, and also the proper rake angle front to back. then the crossmember was tacked in at level side to side and front to back (using the lower control arm bolt in the pivot holes, not a level on the crossmember). then the front end was mocked up using some threaded rod in place of the air bags, and everything was set up to be level at ride height. just to be sure the angles were all correct etc. THEN it dissassembled and was welded in.
anyway, good luck. i think you need the front end assembled and pretty close for wheel alignment, to get the proper wheel backspacing.