Spherical are preferable to plastic - but the whole kit (from Racer's Edge) is $1350 or so. I have mostly spherical stuff. I get the vast majority of my stuff, particularly chassis, from Paragon Products.

Hollow bars are labeled by the effective solid rate; 33mm hollow bars should be larger than 33mm, but equivalent to a solid bar of OD 33mm. I run 34mm hollow bars, but they are slightly larger than 34mm OD. But you and your buddy need to read the rulebook before he spends any money; 944 Spec requires the Spec package, which means 30mm max rear t-bars.

You can't really change the intake either, in ITS. That pesky rule thing.

Header, the ultimate is the Stahl header. Costs $600. Busch are cheaper. Probably not as fast.

You get to run a crank-fire ignition. Apparently that's a wonderful thing to do on these; stock ignition to start, then switch over to a fixed ignition.

RE: bushings - can you think of anywhere on your chassis you'd like to have 20-year-old rubber to race on??? Replace all, of course.

IMO Koni's are too weak for the spring rate needed to really race these; that's why I run custom Bilsteins. Of course, those aren't legal for Spec. I suppose it's a good thing RR shocks aren't legal for IT, or I'd be lusting after a set of Motons; the guys who run NASA and PCA do run those, and they're killer, apparently.

More resources - check out the 944 Spec forums on the NASA Forums. They have a great deal of knowledge there.

JME, Jon Milledge Engineering, is the 944 expert. I hear he's selling off and getting out. If nothing else, get a copy of his prep book - tells you everything about prepping a 944 for ITS racing.

As for suspension and rear torsion bar setup, alignment, etc - get used to it, if you're going to be racing one. Try to set the rear at home and forget it. If you're not continually fiddling with settings, changing bars, or hitting things, you should be able to leave the rear alone. Do so. On the plus side, everything's adjustable stock!