Why are the rear differential bushings different left from right
 

Been playing with the EVO diff inserts (anti tramp) bushings and was wondering why the two rear diff bushings are different in terms of shape and bolts. Is that due to the rotation of the crank shaft?

If you only stiffened one of the two, what would happen? Trying to reduce drive train lash when shifting hard but looking to limit NVH.

I feel I'm similar to you in that I'm a bit sensitive to drivetrain lash, but like to limit NVH. Not sure about the difference in L/R diff bushings. I've got STI engine/trans, WL subframe, and diff bushings. Removed the lower outrigger bushings. Very happy with this setup. Felt the WL trans insert bushing had a bit too much NVH for me.

I have the following Whiteline bushings and/or inserts: Steering Rack, Transmission Mount, Subframe, Differential, Sway Bars. I ended up removing the top and bottom outrigger inserts on the differential due to a clunking sound when shifting. After I removed those the clunk went away and it feels perfect to me.