try on svtperformance.com lots of ppl get rid of them on there, well not lots but quite a few and they switch to solid rear of coruse, make work a trade deal.
Do this go drive a cobra 99 or 01 and slap them gears to the ground. Then go drive a 03-04 Mach 1 and do the same. The result will be pretty self explanitory. The wheel hop on an IRS is ridculous. Plus rebuilding those IRS isn't exactly cheap. Like snake said get one out of an 03-04 go test drive the 2 first. You will see the difference in traction by a mile.