Stock vs. hard plastic vs. solid aluminum are definitely different hardnesses but I really don't think they'll make that much difference in those bushings. Even the stock ones have very little give/play. It is nothing like the front/rear shifter bushings. I'll be doing them anyways, but I really doubt they'll have much of an impact. Like maybe short shift is 70%, shifter bushings are 25%, and the other bushings are 5%. I guess we'll see.
The rear bushing can be done with the exhaust and driveshaft in place. I would remove the tranny "H" brace to have a little more room. Getting the bolts in is a bit tough. You have to keep in mind the that the bolts will NOT be going in straight/perpendicular to the bottom of the bushing. They go in slightly angled. I mentioned this to Kartboy, and they just said deal with it. Lol. Works fine once you get it started, but it's very easy to strip out the threads in the car and then you're hosed.