My '89 2 door Sport was also in need of a better transmission mount so I stepped up and bought SFR engine and transmission mounts. I installed the transmission mount one evening and test drove it. The vibrations were really bad at idle, you could also feel the vibrations through the accelerator pedal at 60 mph. On a positive note, the mount did help to corrected the transfercase/pinion angle issue. Drove it to work and it sucked. The next evening I replaced both engine mounts and modded the drivers side with a die grinder and it was somewhat better at idle and while driving. After 2 weeks of vibrations, I researched and found that 2nd Generation GM F body rear leaf spring bushings are close enough to work. They are slightly thicker in diameter at 1.58" verse 1.5". I removed the mount and in 20 minutes of cutting, drilling, sanding and able to reused the metal sleeve and their now an all rubber version of the poly mounts. It has reduced all the vibrations by at least 50% to me and it was worth the effort for my Daily Driver. I just wanted to share my modification to a great product.
If your interested the all rubber bushings, I used Moog K6560, $17 for 4 bushings on Amazon.