Nope. I can make some educated guesses as to what's different. Suggest you scour the 'net like I did, maybe you'll get lucky & find something I missed.
Can't remember where, bu I've seen some threads about drilling through the Belton plastic to remove a resistor to get rid of the modulation on a BTDR-2, but maybe there were some threads on the 3H as well. Why not throw it on a switch?