I need new diff(s) and need expert advice
 

First of all, a transmission swap is not my preferred route at this point. I plan for 6 DCCD in the future.

My rear diff has play in the yoke/pinion part (where the propshaft connects). This is causing noise, vibration and general mental discomfort. It needs to be replaced.

My current driveline is a EUDM VTD with 3.7 final drive. Finding such diffs is fairly difficult and I'm considering going 3.9 to retain lower RPM while increasing my options. I would like to keep LSD. So here's my questions:

1) How interchangable are the Subaru front diffs, considering my stock 4EAT?
a) Can I use any front diff from any transmission?


2) Exactly what modifications need to be done to an R180 to make it fit?
a) Are there any consequences I need to consider?
b) Do I need to modify the diff itself (i.e Yoke/Pinion) or is it true bolt in? Keep in mind that the input part is the problem on my current diff

3) Are there any 3.7 LSDs available? Some sources claim some USDM WRX came with 3.7.
a) Is there any experience with this?
b) Is this a R160/R180/LSD etc?

4) Are there any cheapo 3.7 non-LSDs that are a direct bolt in?

By and large, I would need the "definitive" advise on what to do. I would also be very happy to receive instructions on front diff swap unless it's fully covered in the service manual.

Thanks