No. The transbrake is a part of the valvebody. If you don't already have one incoporated into your valvebody, you'll have to change this aspect of the transmission.
How high the transbrake will stall is directly related to how big the stall of your converter is although their not usually the same. i.e. you may see higher rpm on the transbrake than you otherwise would on the footbrake.
Maybe, maybe not. You could have your box pulled apart and the valvebody replaced and see how you go rpm-wise but if you want to stall it much, much higher than the 2500rpm you're currently set up with, you will almost certainly have to change converter.