The driveshaft. I stuck with the stock 318ti driveshaft and it does physically fit. I had to compress it as much as possible and drop the center support bearing to get the shaft to slip into place on the trans output flange. I wasn't super thrilled with how tight it felt but it does work.
As for the rest of the drive train, I am already running a 3.73 Medium case diff and using the stock 318ti axles. I plan to rebuild the pair of E30 axles I have and swap them in. I'd like to eventually get a 3.46 diff since that will work better with the short tires I run.
My current gearing/diff/tire setup should be good for the speeds I'll see at VIR. I'm not sure what to expect at the end of the back straight though.
Got the core support back in place so I could mount the radiator. The S54 Z3 rad drops in place nicely, just make sure to swap the lower radiator mount and move the top clip over a few inches.
Around this point I discovered that the throttle body that came with the engine had been damaged upon removal. The clips that hold the cables in place were both damaged and the cruise control plastic was severely missing. Found a replacement on ebay for $30 shipped and it was delivered a few days later, clean and complete.
Got the intake manifold, vacuum hoses, fuel rail, and throttle body installed.
It's starting to look like a real car. At this point there wasn't much left. I remounted the bumper, headlights, and nose panel. Make sure to get all of the plastic ducting in place behind the bumper, it is very important to adequately force the air through the radiator.
Hoses to the radiator were straightforward. I used 5/16" heater hose to run from the rad to the expansion tank. Then I used a small hose routed down behind the front wheel to vent the expansion tank.
Next up was the exhaust. This proved to be more of a pain than I initially expected. I'm using the stock M52 headers, to the stock midpipe, to a Z3 3.0 catback. Dear lord, that midpipe is heavy. The hangers bolt right on under the heat shield brace near the ti fuel tank. Then the two rubber mounts hold the midpipe in place very nicely.
The fun part is that the Z3 exhaust is two 50mm pipes and the 328 midpipe is two 48mm pipes. Otherwise known as 2" and 1 7/8".
Here's a picture of the amount of Z3 exhaust that I got. I cut the midpipe back to be a couple inches from the rear hanger. This length was almost perfect, just hanging both the midpipe and muffler section, there was maybe a 2" gap. Easily able to close that up with some adjustments.
I planned to use 50mm clamps that is a BMW part for the Z3s. However, the clamp tightens to just under 50mm. 48mm slips right out. Pic below.
I ended up ordering two exhaust adapters that go from 1 7/8" ID to 2" ID. I will weld the adapter to the midpipe and will clamp the muffler side with torc tite clamps.
One thing I discovered, I bought the cheap version of the exhaust hangers and not the OE BMW hangers. There is a huge difference. cheap hangers are cheap for a reason, the rubber is much less resilient and allows too much play so you get the exhaust swinging around. OE BMW hangers actually keep the muffler fairly rigidly mounted under the car. They do cost more but I found it worth it.