I was wondering about that also and here is what i found. On www.ttcautomotive.com
(search the Tremec pages)they list all the different gear ratios and depending on which one you find it could be good for up to 450 ft lbs. of torque.I have read a few articles in different magazes and found this transmission has been used in some 10 and 11 second cars. Well i read enough praise to install one in my newest project .I have not had the pleasure of driving it yet but the anticipation is killing me.
Weir Hot Rod products out of California, 800-633-9869 , last ime i checked ,was the only people who made a product to help the swap . I bought one for my 70 Chevelle big block project. It is a sweet peice, it comes with everything, hydraulic througout bearing and master. I paid @ $570.00 U.S. the Richmond 6 spd is rated also at 450 ft lbs i beleive, and it is a direct replacement for a four speed, but is quite pricey.
I chatted on ,a chevelle page i frequent , to a fella who had done this swap in a big block Monte and he had nothing bad to say about it . He claimed it to be one of the best upgrades he had done. Hope this helps. Have a good day! :-)