http://users.tpg.com.au/users/loats/...gearboxes.html
If its a gbox from a 4wd truck, you wont be able to use it, the gearset is differant (W56) and it has a transmission casing bolted to the back.
You want a cressida W57/5 (just differant gearsets), they are midmounted. If you wanted to run a 58 a mid mounted shifter should be able to be fitted.
As for C/Ps and P/Ps they are all the same throughout the W5* series boxes all are 22spline (90% sure on the spline count), i advise to use a 9" hilux clutch, its more heavy duty than the supra but this depends on what flywheel you will be using.(i have 2 hilux a supra and two rwd celicas all running the same clutch setup, i buy clutchs in bulk, lol).
Not sure on what you mean by a 89 celica box? as far as i'm aware they run a C5* gearbox which is not appropriate for your situation.
What flywheel will you be running? If its a jag one, I'm not sure if the bolt pattern of the toyota P/P will match or if jag put out a c/p with a 22 spline count, you'd have to research that.