What rear subframe/suspension

With the announcement of the 2014 Challenge basically in my backyard, I have started looking at the Spitfire again and what can do to improve it. I had originally modified the frame and used a TR7 solid axle with shortened trailing arms and motorcycle coilover shocks as a cheap and effective way to handle the power of the turbo ford engine (close to 300 HP). My plan for 2014 is to weld in a cage to support an IRS rear subframe and suspension from hub to hub and make a suitable drive shaft to mate the T5 to ???

So any ideas here, preferably one that is compact (and narrow for fitting under the Spitfire body, but with my fender flairs this is not too much of an issue), capable of supporting the HP and Torque of the TurboFord engine, and cheap. Limited Slip would be really nice. Did I mention that it needs to be cheap?

Thunderbird

Miata

Maybe a 924/944? Rear suspension is a self-contained unit. You'd have to come up with your own differential housing (an Audi quattro rear diff perhaps?) but it will handle the power and has been used successfully in racing with similar power levels. Not sure the width would fit the Spitfire body/chassis though.

In reply to dherr:

I have a RX7 TT IRS and a spare center and axles.
Andrew

how much power can a subaru rear hold? might be able to work something out of one. (especially try contacting FFR 818 builders, they won't need one)

I had thought about a miata as the first natural choice but wanted to consider other options. Width not a big issue unless we are talking crazy wide (for example the Thunderbird would stick out 6 inches on each side (I know what you are thinking, what is wrong with that??). Andy - do you just have the pumpkin and axles or an entire IRS with rear brakes?

You want to fab your own control arms or just plop something in?

I would prefer to plop something in so I can just fab up the coilovers and move on to other pieces of the car but I am open to suggestions if it is worth the time, meaning it saves me budget money or buys me more performance

T-bird pumpkin and Miata A-arms seems to be the low cost leader. The Caddy CTS pumpkin is desirable but seems to add to the cost.

That said, I have a hard time seeing it done for less than $700 unless you can broach the hubs yourself; that is a big chunk of the budget.

In a contest such as the challenge, I don't see the IRS bringing enough to the table to make it worth the effort or budget. Certainly the drags favor a solid rear axle. And unless the slalom course is rough, hardly an advantage to be had there.

Now, form a "Kool factor," yeah...that would score some points.