I mocked it up in wood first, then welded up the three main pieces; side rails and cross-member.

Then, I bolt the front of the side rails through the forward leaf spring hard points, and swing up the rear

Once in place, I use the original shackle links to pin the rear in place.

Then, added the anti-sway bar. If you notice, there's still about an inch left on the bolt where the original Jag radius arms attached. My future plan is to build Watts linkage style radius arms (going straight forward and aft to the chassis, with a pivot at that bolt) to react the loads at the LCA.

By the wat, just for kicks, I had one of the local high school geniuses do this whole thing in CAD (Inventor), and made a few adaptations on the as-built. Here are my starting dimensions (elevation view).

Here she is today.

And a Mustang II front clip.

I do not see any signs of narrowing on your IRS. Did you leave it at the XJ6/12 width?
 

For Tyrell Racing. Correct. The '67/'68 is two inches wider flange-to-flange than the '65/'66. I didn't shorten the LCA or half shafts. What I did need tho', was wheels as follows: 16"x8"x5.25" BS Torq Thrust.
Note the large backspacing. That pulled my rear wheels back in. Since the Jag IRS is a Chevy bolt pattern, and I wanted same wheels all around, I needed wheel adapters in the front, to go from Ford to Chevy. So, I got the 1" thk wheel adapters in front, and the high backspace wheels with Chevy bolt pattern all around. Long winded answer, but I hope you get it.

So will you email me every thing you have?

got it, Thanks!!!

Follow-up: The '68 Mustang, "1FSTPNY", has been "out-and-about" for 6 months now. After a few hundred miles of "test flights" and some slight suspension tuning I went up to an autocross being held at Shelton (WA) airport. I decided, "If I'm gonna break 'er, I'm gonna do it today". And proceeded to mash the course. Man, the results give me a rush of pride, and same should go for you! Absolutely exceeded my expectations. With the locker rear end, she grabbed the course and just tore it up. Flat, solid and steady even around the tightest turns at each end. Just a little over-steer, perfect for feeling a nice, smooth, controlled transition as traction slips. No jump, shudder or hopping, at all. I can get the rear to come around nicely and set up for the straights. The slaloms were tight, with almost zero body roll. The TCP frame connectors locked the chassis; front to rear, and the Mustang II coils overs with rack & pinion in front .... altogether a fine driving experience!
NOTE - The aluminum torque arms began getting loose in the threads, so I went with steel. Also added side plates over, and just outside, the wheel arch (belt and suspenders) just to add some stiffness in that high stress area of the side rails. Final weight distribution, with full tank of gas and driver, is 51% Front, 49% rear.