We weren't sure which rear end to build in the kit, but the IRS is the option that almost everyone keeps telling us to use.  Since the car is going to be a daily driver, a good ride will certainly return dividends over time.  Here is a picture of the Factory Five IRS:

We picked up a 1994 T-Bird IRS which will go into the Roadster.  My brother already knew someone who had several Thunderbirds for parts, and we picked up the whole unit for only $100.  He is making this way too easy.

I'll add the pictures of our IRS parts soon.