Kevin:

I just completed a project that has a few similarities and I can offer a little bit of advice here and there:

1. I would opt for a differential from a 300. I left the one in from my 240 (donar car) and it is screaming at 70 mph. It has a 300DT to push it (and a manual). Gets out of the hole nice but doesn't have anywhere to go. Apparently the '85 had the best ratio for a differential. Eventually I'll throw the one in from my mangled '83 300D simply because I have it and its free.

2. I echo what someone else said. Get a different driveshaft unless you are certain you can fix your center bearing issue. Mine also came apart (unmarked) and I was fortunate, because 1000 miles on the road so far and its working well.

3. Regarding radiator and oil cooler:

a. I put the larger one in from the 300 along with its oil cooler mate and i'm please with it.
b. On another of my 300D's, I just replaced the radiator with one from a euro 300 and didn't pay attention enough to its size. It ended up being wider so I also had to replace the oil cooler with a narrower one. This may prove to be a bummer once summer comes. But summer only comes between July 7 and July 14 in Michigan.

4. Can't help with the transmission cooler lines. I simply cut mine cuz its now a manual.

Don

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DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed