Nice Plan!!
I had the same dilemma, yeah looks hard/expensive to find a exhaust mani for a fit. Sounds like the most involved part of your plans, but probably would be worth it to DIY. People will hate, of course it won't flow as well as a "real" one. At the end of the day, you got a solution to the problem for like 50 bux vs 500+. A while back, it was hard finding cheap t3 manifolds for G54B motors, so I found a ka24de t3 manifold (ebay) and the runners seemed to match up. We used 2 flanges: 1 for the 240, the other for the starion and just made a "conversion adapter" with runners in between them. I'll try to find pics
5 minute task, loosen compressor/exhaust housing, spin, tighten so the drain goes straight down.
I'd just save up and go to an exhaust shop for this- but if you're DIYing go for it
Can't use it, your car uses some crazy hi-tech stuff they didn't have back then. That looks to be a possibly chipped obd1 computer with an obd2 conversion harness. You can probably sell that ECU/harness together for ~100 bux if you can confirm it's chipped.