Anything is possible with either time or money or effort.
I seem to recall somewhere on the interweb is a blog about a guy who adapted an IRS system underneath his early A body. He did it as a budget exercise, relatively speaking, and sourced most parts from salvage yards and did his own fabrication. I seem to recall the end results produced a smoother ride, which was his goal. He didn't push the car much as a performance ride so he had not idea how much better it performed just said it felt better. Is that the truth, probably. I can't discount his butt-meter any more than I can call mine a benchmark. I do believe since his IRS was sourced using late model Ford parts, he had access to improved shock systems and was using better matched spring rates, which likely contributed considerably to the improvements, so similar results could have been achieved with less cost, effort, and time using a bolt on set of parts from a package supplier, but that wasn't what he wanted to do. Will an IRS ultimately outperform a live axle, it certainly can. Do they look impressive, hell yeah! So if wow is the objective, its hard to beat. If fab time to test your skills is a concern, it will live up to that to.
Check this IRS from Freak Ride. I'm installing this in my 1970 Challenger:
http://www.freakride.com/2013_mopar.pdf
Cost is $1800 which I think is reasonable considering you'd pay just a little less for the Hotchkiss leaf spring kit but you get a superior 4-link instead. Only welding required is for the crossmember between the rear frame rails. This is the setup used in the Mr. Norm's GSS Darts.
Those are four link systems, not IRS systems.
