Ok,

We built a 2003 IS300 Twin Turbo back in 03-04. The tech that built it is no longer here, and it's a nightmare. My GM just asked me to jump in and help.
This car is suppose to have a Turbo Supra driveline in it. I pulled the numbers off the trans casing and the driveshaft.

I tried to have our Parts Department help out, but no luck. Does anyone know where I get the info I need to verify? I tried to Google, but no luck, and our parts store online doesn't seem to find the numbers I have.

Yeah, the IS300 does have the same engine/tranny from what I remember. Have you tried the Supra forums? http://www.supraforums.com/forum/ and www.MKIV.com

Im on the Supra forums. So a IS300 uses the same trans that would be found in a 92 Supra??

Oh ok cool.

No, it used the 93-98 Supra driveline aka MKIV. 92 is the last year of the MKIII.

See this and look at the 2JZ-GE:
http://en.wikipedia.org/wiki/Toyota_JZ_engine

and Supra MKIV engines/transmissions:
http://en.wikipedia.org/wiki/Toyota_Supra#Mark_IV_.281993-2002.29