Yes, I am using a Jap spec T-50 Levin box but this is the same in dimension to the Oz T-50. I didn't have to measure it as my mechanic did all the work. I'm in Queensland so if you're up here, I can get you the details of the people who did the job for me.
Just be wary because it's not the size of the 2 piece drive-shaft given that it is angled when in (if that makes sense). The first time it was made, it was too long but we had them resize it again.
If anything, check out Bill Sherwood's site at www.billzilla.org
under the motoring section. There is one particular section where he mentions the process of converting a Sprinter 2 piece drive shaft into a single one.
BTW, T-50 gearboxes apparently don't last long when mixed to a 4AGZE. You're best off using a Supra W-55 box for the job from what I've heard on the net.