The fronts will definitely work, but the rears may be an issue. I haven't seen the strutmasters kit for the MarkVIII, but I know for MarkVII and some other cars, the spring gets bolted to the perch, which requires the conversion springs to have a smaller top and bottom coil. The springs designed for a tbird won't have that. If your current coil springs are held in that way, then you won't be able to run tbird springs without a pair of upper and lower perches. When I converted my car over to the eibachs, I used the upper spring perches out of a tbird, and welded them in place on the MarkVIII, and for the lowers I cut the perch out of a pair of stamped steel control arms, which were only on the 89 tbirds and cougars, and I welded a pipe to the center inside of them to locate them in the hole in the bottom of the MarkVIII LCA. If you don't want to go through all that work for the lowers, get a set of the UHMW lower mounts from DLF, but for the uppers I would definitely reccomend cutting a pair of upper perches off a tbird or cougar. The MarkVIII upper perches are perfectly flat where the airbag sits, so you can cut the tbird perches off anywhere above that, then just trim them down to the flat area, make sure they are lined up, and weld them in, and you'll never have to worry about it.
-91 Cougar LS, coming soon, complete overhaul
with a 427" Windsor.
-90 XR7 5-speed black on black w/sunroof, MP2, coated rotors, double intercooler, 15%OD, ported heads, comp stage 1 cam, 85mm TB, 90MM LMAF, 80# injectors, and ported big valve heads
-98 Mark VIII LSC, Procharger P600b, TR3650 swap and 3.73s.
-90 SC Automatic rustbucket winter beater
-97 Tbird Sport 4.6 Nice weather daily driver
-"Your buddy Mike is INSANE!" -ClintD's dad