Welcome to the board. As far as the aircleaner situation, getting a drop base 14" aircleaner, say from K&N, with a 1 1/2" to 1 5/8" base drop should fit under the hood. The rear end diff is easy. check out the drive train section here, there'a a sticky with pictures that show the difference's between the R180 and the R200 diffs> Good luck and happy motoring!