I'm afraid I can't help with specifics about the exhaust brake, but Gary has already provided some manufacturers to check with. Regarding the lock-up torque converter however, maybe I can shed some light on that. As you know, a torque converter has a internal rotor and an external stator (the converter housing), both having blades like a fan, or more accurately like a jet engine. The rotor and stator are not directly coupled, but are immersed in transmission fluid. Thus the rotor, turned by the engine, starts the transmission fluid swirling, which in turn spins the stator, and consequently the transmission gears, driveshaft, rear end, and finally the drive wheels. This fluid coupling is not perfect and some slippage occurs. The newer lock-up torque converters will actually lock the rotor and stator together physically under controlled conditions, to eliminate this slippage. As you might expect, a torque converter can work in reverse too, the rear wheels transmitting power to the engine when decelerating with your foot off of the gas. If you have an older style, non-lock-up converter (doubtful), the exhaust brake will still work with it and provide engine braking - maybe not quite as much, but it will still get the job done.
A suggestion: Maybe you do this already, but it is recommended that when going down steep grades, short, moderate application of the brakes should be used to control speed rather than light, constant application. Sometimes even heavy applications are needed, but this will allow the rotors to cool between brake application and will help prevent rotor warpage and fading.
