Kind of slapped together
Join Date: Jan 2010
Location: Bossier City, LA
1) The 8.8 is a sound rear end; it fits behind even beefier Mustangs today, so it's got the possibility. I WOULD ...
2) Recommend a complete rebuild, using the carbon fiber pack out of a IRS Cobra 8.8 rebuild kit for the traclok differential. Also, all new bushings. Plus look at the gear ratio; if it was a standard, the gear is a stock 2.73 (!!) due to the rock crusher 1st gear in the M5R2 5 speed used on the manual SCs.
3) With a truck chassis, I'd look hard at Delrin bushings around; Jay Richmond (98mark8lsc here, Jay Richmond on Facebook) makes Delrin bushings for the spindles to the control arms and the subframe to the body/chassis; SuperCoupePerformance amongst others has a nice beefy poly rear diff mount for the IRS differential; also a LPW rear cover that's a bit beefier.
4) Stuff as I listed above; also, the wheel pattern on a stock hub for a MN12 is rather sucky for wheel choices and won't match the hubs on the Crown Vic front. I don't know off hand what you can do on the Crown Vic end, but for this end, you can also consider converting to the Mustang bolt pattern (Cobra hubs, a set of relocation brackets for the calipers, and even a set of Cobra calipers to go with the Cobra rotor); I don't know how that will match the front, however. *googles* Oh, the Crown Vic and the turn of the century Mustang uses the same bolt pattern; that's nice, a Mustang/Cobra hub swap on the back will make the wheels matchable.
5) Hub bearings should be redone; see #4's notes on the Mustang/Cobra hub pattern (you can redrill the MN12 hubs, or use Cobra hubs, kind of your pick; to use the MN12 brakes, you'll have to have the rotors redrilled, and to use the Cobra brakes, you'll have to pick up a caliper relocation bracket set. STILL cheaper than trying to find a Cobra IRS from what Googling I can do ... ) Also, see note about getting that diff rebuilt to be rock solid. It should be good for > 1,000 HP with an automatic; if you're really serious about planting it, though, you might want to consider some custom made half-shafts since a firmly planted manual launch can pop the half-shafts on these (the automatic kind of "spools up" through the torque converter, so it's just enough softer to let the IRS launch; dumping the clutch on the manual can shock load it and bust them.)
There's actually a guy over on SCCoA.COM that did a 3.8SC and the IRS in his F100 (IIRC); might want to check over there also.
ALSO. If you're transplanting the entire rear subframe, there's a gotcha on the UCA/subframe bushing; check the posts over in the suspension subforum to help make sure you get the RIGHT one instead of the non-adjustable Piece of Stuff that most folks sell nowadays.
Delrin bushings on the knuckle, delrin LCA/subframe bushings, and you'll take care of most of the "wheel hop" some folks complain about.