Yes, but will a tremec hold up to a 600 HP Big Block? I think not. Also, can you install a Tremec without cutting the floor? Umm no.
The Passon Performance 5 Speed offers a number of advantages, among these are 1) stronger than an 18 spline 833, (Passon is putting the torque capacity at 650 Ft Lbs, in testing he abused the transmission so badly that he BENT the unitized body and had to stop testing to install sub frame connectors in his test mule, the transmission didn't break however) 2) absolute bolt in assembly 3) absolutely stock shifter location.
The Passon Transmission is LONG overdue, but somethings are worth the wait. Also, for someone who already has a car with an 833 the price differential is negligible since they will be able to reuse their existing cluth, pressure plate, bell housing, throw out bearing etc. Witha Keisler setup you have to rebuy all of that existing hardware pushing your total cost past 4K.