Ive read somewheres they can handle up to 330-350 ft/lbs of torque, before they break.
I cant remember the website that has the flowchart, describing this, and what to do about it, so it can handle.
Heres a site that talks about something about the tranny:
http://www.highperformancecars.com/crosley/drvshell.htm
Heres another:
http://www.transmissioncenter.net/70...rque_Drive.htm
EDIT: Here it is:
http://www.700r4.com 
Robert