It takes quite a bit of both time and money. i have been looking to do the same thing on my scamp. just to find a decent IRS it can be around a grand then you have to find the right length axels and modify the cross bar that connects it to the bottom of the car and then align everything, there were some other things to buy and do but they slip my mind at the moment. While i was looking i found that even though they arent mopar a jag ar vette IRS is stronger as well as a bit more affordable because there are a lot more of them being as both of those companies have been using them for a while. you can also look online for a custom hot rod style one if you got the money. theyre a bit more expensive but you send them measurements and they build them for ya so it wilol fit when ya get it provided that you made the right measurements.
im still probably gonna do it but not for a while there are more important things i need to get for the car right now for me to spend the money.
pm me and i can look for some places i got the names from and send em to ya ;)
good luck
-marc