Measure from the flange where the tail housing bolts to the body of the trans, out to the end of the tail. I'll bet yours is probably a 6" though. You also need a torque arm bracket, which moves the mount off the trans and onto the body. T350's don't have that torque arm provision like your 700R4 does.
Looks like this: http://www.summitracing.com/parts/BM...ion+Type|TH350

 

Yup mine is a 6 inch tailshaft. So i'll need a torque arm bracket, driveshaft, and cross memebers. I've heard people tell me that they have used stock cross memeber before but it's hard to do sometimes. Do you recommend just buying a new set for the swap? And that's everything i need correct?

 

heres a crossmember for 140 bucks, part #50f its about 2/3 s way down the page.
http://www.transmissioncenter.net/35...rmance%20Parts

 

Just get the torque arm relocation cross member from UMI:

http://www.umiperformance.com/catalo...avo9fn19qvbjh2

 

Both the BMR and UMI units do the same thing, they are a combo trans crossmember/torque arm mount. To me, the BMR piece at Summit looks like it has a beefier trans mount tongue.
So to answer your question Sinclairaity, no you don't need to also buy a separate crossmember, those that we showed you do both.

 

Sorry, I didn't realize you posted a link to the BMR piece. I thought people were still discussing using a relocation bracket on the stock cross member.

BMR, UMI, and Spohn all make nice cross members, but I'm partial to UMI because of their quality and customer service.