I did a bunch of research on this subject several months ago, and here's what I came up with:
The celica (ae86, right???) struts are about 0.05" longer than the Supra.
While there's a bunch of other struts that will fit in our Soups, the whole problem is weight distribution, damping rate and rebound rate will not be quite matched to our soups. This shouldn't be a problem for the majority of folks on this forum, as most don't autocross or roadrace their vehicles, and would never push their car to the limit where these areas become critical, but folks like Billy and myself (and several others I can't remember right now, you know who you are!) do happen to race these cars.
Even with TRD adjustables on the rear of my car, and GR2's on the front (that are specifically made for the MKII), the car is incredibly unbalanced on the track at high speed cornering! Coming into turn 8 at Willow Springs Race track, at around 75mph, the suspension is under so much force that the car starts cavitating front to rear because of the mismatch in damping from front to rear. Now, add in another vehicle's strut that's valved for a different weight, you'll find an even worse imbalance!
I'm not trying to discourage anyone who's thinking of using other vehicle-specific struts/shocks, but I do want y'all to know that it really is tricky to get a setup that really works well!
From what I know, there's a certain rate of pressure introduced to the strut at any given time, and this is compensated for by the valving of the strut. The amount of damping is based on the weight of the vehicle, and as you corner/brake, this pressure is increased, which the damping is to compensate for, thus keeping the suspension from compressing/rebounding too much (which upsets the balance of the vehicle, as well as the camber as it lifts/compresses).
Even with just a 100lb. difference between 2 separate vehicles will produce a different characteristic in handling! And, we haven't even added into the calculation the front to rear weight distribution! for example, a 50/50 distribution while braking will add (theoretically) 700 lbs. of EXTRA force to the front struts, change the distribution to 45/65, and you can add another 300 lbs. to that number, even if the weight of both vehicles are exactly the same!!!
So, the big question we should all be asking is, will another vehicle's struts/shocks work better than the best available strut/shock made for our vehicle???
Dammit! I'm always posting way too much! Sorry folks...