I don't know how much space is between the back of the engine and the firewall in the supras, but in my cressida I was able to get access to the top bolts by removing the gearbox crossmember and supporting the gearbox on a floor jack, then slowly lowering it until it got as low as it possibly could. I was worried about straining the engine mounts, but several thousand miles later and they're still good.
This created enough room to use 3 feet worth of non-wobble extensions to remove the two top bell housing bolts. From personal experience, a bare minimum of 900 mm of extensions would be required, so almost 3 ft. You may want to put something thin yet tough behind the cylinder head in case there are pointy bits that might poke into the insulation, as is what happened with mine when the rear coolant hose's spring clamp tore a hole in it.
Even though the extensions were non-wobble, there was still enough play in them that they gently curved over the distance, but tilting the whole engine+gearbox without loosening the engine mounts, there was still enough room for the 3 ft worth of extensions to be ramrod straight, which was a bonus because those bolts were stuck, and there was no room for an impact. I just decided that I myself was the impact wrench, and wailed on each bolt for about half a minute or so until they finally loosened up.
The upper starter bolt can be accessed as well doing this. The lower one I got to from beneath the engine. The nuts were a pain in the ass due to the lack of space to get a wrench to hold them in place while I loosened the bolts.
If you don't have a rear main seal puller, get a long screw (at least 50mm long) for screwing into metal, filedown the end so it's blunt, then drill a pilot hole into the seal between the sides of the seal (you don't want to damage that, the section between the crank and the housing is fair game) then while keeping the screw as straight as you can, screw it down and keep turning it, you should eventually feel it bottoming out, keep turning and it should slowly push the seal out. Then use that old seal to hammer the new one in, don't forget to lube up the sides of the new seal with a coat of oil.
If replacing the gearbox output shaft seal and like above don't have a dedicated seal puller,
and are taking the gearbox apart, you can take off the rear half, hammer off the dust shield, then grab a crowbar and wedge it under the seal then hammer it out. Alternatively, just buy one of those seal pullers, never used one myself, but apparently "it just works."
I remember when I pulled my w58 I used 2 skateboards and floor jack lol. Would have been so much nicer to have a transmission jack I would highly recommend renting one. Also put down a tarp or something just incase a little fluid comes out the tail end. Don't know if you'll need it but I also put a new rear main seal when I did mine since the transmission was out of the way already.
I dropped my old auto using the floor jack, and then while I was lowering it I forgot about the radiator lines and it fell off...managed to drag it out far enough to get the bell housing on an old creeper, then the output shaft on a dolly. Never again. After that fiasco the alloy W58 was a walk in the park, relatively speaking. Just ended up lifting it on the same floor jack, then when it was close enough, rested the rear half on my knees, while bench pressing and wrestling the gearbox into position. It was surprisingly easy doing it this way.
Yes that'll happen with the W58 or the R154 so drain your gear oil.
