Thanks to everyone I've asked to about this swap, your help is greatly appreciated.
Here's the gist of it for anyone interested:
RA28 W50 into RT104 w/ W40 18R-c
-Bellhousing fits perfectly
-Clutch slave cylinder is interchangeable
-speedo drive plugs in - although speed may be off, use a GPS to verify
-Reverse lamp switch plugs in, works fine
-input shaft lines up correctly
-clutch/flywheel/pressure plate interchangeable
-prop shaft fits with no mods
-W40 crossmember works with W50.
-Starter motor interchangeable.
-Light enough to bench transmission into place (although I wouldn't recommend this)
-Gear shift stick interchangeable.
- Shifter location housing is not interchangeable between W40 and W50
-Celica shifter location is further forward 2.5-3", but a small hole further forward is all that is required.
-Shift boot and locating screws need to be further forward
-W40 shifter is too far forward and you need to lean forward for 1,3,5
Verdict: Pretty much the same shift points as the W40, yet to test the top speed but should be higher (W40: 130-140 Kph, W50: ??) Good gearbox, much better on the highway.
_________________Choosing an old car doesn't have to mean you're on your own.