on it. It's about 4" long and connects to the swing arm at a 90 degree angle. Can this be removed to stiffen the bar? If not, are there any sources for slightly stiffer bars?

I do not know if the piece can be removed. I also do not believe there are any stiffer bars available. I could be wrong about all of the above BUT I do know that the rear bar was ONLY available on the 92 model, not anytime else, so the target market would be absolutely miniscule (as if it isn't already small enough) for different bars. Perhaps have one fabricated to your spec?
Jim
93S4.