Hi Clois,
It may not help you much, but I did convert my E-M from leaf spring to Jag IRS. In my case I was able to go to E-M and get the drawings that they use for their Jag cars along with the parts that I needed for the conversion. Since their frame is/was available setup for the Jag it was very straight forward when it came to the conversion. Just cut out the old mount points and weld in the new parts. Alignment was easy by dropping a plumb bob from points on the frame and making marks on the garage floor, then shifting things around until it was just right. I did deviate from their design by using radius rods rather than the forward mounted control arms that they use. With the E-M you could do the conversion with the body on, but it would be alot less fun..........
My car is not done yet so I can't comment on the live vs IRS performance, but the Jag IRS does look alot better than the leaf spring
.
Good luck!
Jon