[Lowell W]

Lots of good info above.

One slight correction: SPF did use the Ford 8.8-based IRS but the newer cars have an Australian (I believe) Dana IRS. Not sure how this compares to the Ford strength-wise, but apparently Ford has stopped producing the 8.8 IRS so SPF had to source their parts from another manufacturer.

There's a good article on Ford 8.8 rears in the current (Marked "June" but who are they kiddin'?) issue of Car Craft. It compares the relative strengths of the 8.8 and 9" Ford and 12 bolt GM axles and has suggestions for mods. The gist of it all is that you can upgrade the 8.8 to 31 spline axles and diff, giving you 30% more torque capability. BUT...you can build the car now with the 28 spline axles and upgrade later if you break something or make more power.

A few observations: The original cars used IRS. I've read or seen in print that, since these cars have such short driveshafts, suspension travel with a solid rear is necessarily rather limited. Also, point well taken that the IRS will add more to the value of the finished car when it comes time to sell it. The IRS may also be a little lighter, with an aluminum center section, although the axles are heavier...may be a wash.

If I were building the car, I'd go for the IRS upgrade initially and sacrifice somewhere else, if necessary.

Good luck with your build.

Lowell