Posts 3712, 3713, 3724 and 3774 give you the info to dial in 17 by 10's on 285's at the back without any tubbing.
Do that first. Zero off your costs, Dave.
Before I wrecked my 81, I measured up Ferrari Testa Rossa 240's and 280/45VR415 Michelin TRX's, a tire a lot wider than the indicated width. Its basically the same as quadra shocking it for space, since its uses the inner stabilizer shocker mounts.
Everything fitted in with stock parts except the rear needed thin bolts and 6.5 mm spacers to clear the modified 16 x 10's. (Down hand Welded by adding aluminum by TIG...It's only 170 thou max of welded in metal, and a release angle taper to turn an Imperial 16 x 10 wheel into a Metric TRX 415 TR255. I got the tires from a Ferrari TR).
Everything Nissan Skyline (based on the 240SX platform) is pretty much ET35, or 6.88 back space at a 10 Inch wheel size. They look great on Cobras, and you don't have any of the crazy lard a$$ wheel eyebrows like Ford added to the New Edges. Everyone want to copy them down to the Four Eyes and Aeros, and thats cool if thats your bag, but flares are so Wooden and boring, IMHO. They can look awesome, but its gotta suit. I like IMSA's and some M81's, but some flares don't gell with me. Your car, your itch to scrathc, YRMV. You gotta own it Dave. Royal Order of the Box Head....
The extra tire space comes from the removal of the Curved Y tube upright, and Ford made the U section that way to absorb side impacts as well as using the exiting Quad shocker mounting bolts as found on 84-1/2 onwards Mustangs and Capris, and the S shell Tbirds and Cougars.
The anti roll bar relocation is easy, and the upper U tube mount is just the way it is so that FoMoCo didn't have to redrill another Fox frame rail. You can shift the Upper U tube inwards, and the upper and lower gusset could be made inbox section and frame mounted another way.. I'd say that a forged alloy component that mounted on a slip tube over the left and right fram rail would make another 25 mm of tire width. Canting coil overs inwards would make a lot more room than just 305's, and you could make the chassis rails a plinth to hold a cut down Upper U tube.
For example, when Ford Australia slapped the IRS into the Falcon 1998, it used the 1982 Watts Link Coil spring frame rails, and the same kind of IRS.
The ages old leaf spring front eyelet was used to hold the lower control arm with the six link Watts linkage, coil spring axle. The IRS conversion used the same basic pressing, and the IRS cradle was held with an additional mount between the old SRA's two upper and lower arm "eyelets"
Ford of Australian and FoMoCo in the USA had differing axle centers, with differing frames, and there is no real way to ever standardise on one set of components. In a similar way, even with similar 7.5 or 8.8" diff centers, everything in the MN12, Explorer and New Edge Stang IRS weren't in any way similar to each other, or the 1998-2002 or 2003-2016 Falcon IRS systems. Anytime Ford in any country tried to standadise parts, the application then became massively expensive.
The 1998-2002 uses AVO 15" coil overs, kinda like Carmicheal Angelo's, and a compact 7.5-7-7/8-8" 9 bolt Camaro G52 center made from ancient patents dating back to 1966 by Borg Warner Australia for the Chrysler Valiant and Aussie 1966 Falcon. Its the same size as the 7.5" axle center used in some MN12's. The whole shotting match is easily fitted up to a Factory Five Cobra,
Note Dave that it uses angled inwards spring damper units, a forward mounted anti roll bar, and you need to just think do minimum to kick start a good IRS.
The Aussie IRS still uses non solid mountings.
