The 4L30e is a weak link but not necessarily because of it's torque rating. The failures seem to be associated with solenoids etc. I would highly suggest doing a 5 spd swap though and the AR5 is a pretty rugged option that allows you to maintain TOD.
The bolt pattern is 60^ GM for 4L30e and AR5.
Everything I've seen shows the 3800 using the same bolt pattern.
http://en.wikipedia.org/wiki/List_of...using_patterns