I have looked into tubbing the Cougar, and I believe the cost would be very similar to just have it changed to solid axle. I was quoted $2500 just to build the steel subframe in the rear. The you have to price your rear-end, 4 link bars, and everything. I'd agree it would only be worth it if you were going to make a full drag-car, gut, tub, and tube chassis. There are plenty of people putting a lot of HP through the IRS. Make sure you get a guarantee that the chassis will pass NHRA tech to a certain time before you get started, that's the only way you are going to know you get a quality job. The guy who's building my chassis for my drag car has the inspector come look at the chassis after every step to insure that he won't have to redo it, and that It'll tech to 7.50's in the quarter. If a builder is not willing to include NHRA certification in his price, then he's not the one to be working on my car, I've seen too many cheap backhalf jobs break exactly that, the backhalf. Either that, or the first time they get to the track, the car is so uncontrollable, because the suspension geometry isn't right, that they have to almost start over again.