the biggest thing with the upright is, it's f**ken easy to change the starter motor. :D
there is big hp and torque gains from standing the engine upright, alot of it comes down to the intake runner length. but as jamie said oil return is one of the advantages.
the upright kits are non existent, even we couldn't get a TRD bell housing, but we did get a K-t one with cable setup for the clutch.
there is alot of work to standing them upright, engine mounts,gearbox, mount, oil pump and pickup, extractors,inlet manifolds and base plate,sump,rad hoses,gearstick and there is some other little bits as well.
we've had this upright since 1989, and has been the best thing we done to the engine, not only for performance but for changing things quickly
(much needed in rallys).
i know that we brought the last kit in NZ but i have heard of copies being made.
for me the holy grale would be to find a TRD bell housing, maybe one day!!!
if your in brisbane, we have rally coming up in the next couple of weeks, come and have a look and i'll try to answer any questions you might have.