I don't post on this forum with any frequency as there are many people on here with vast, and I do mean vast, technical knowledge pertaining to Bridgestone motorcycles. These bikes were however my main source of transport from the late sixties through 1973.
The brakes were of extreme importance as I had little use for speed limits. (They're kinda just suggestions after all.) The rear brake is useful, although marginally if the front brake is being used hard as the weight transfers forward. I suspect that a twin leading shoe rear brake, with its self-energizing tendencies may be prone to lock-up, especially in a panic stop. If the shoes are properly arced to the drum, which they are not until worn in unless this procedure has been performed by one the the shops that specialize in that procedure the standard brakes are more than adequate for a bike of the weight and performance of the GTR. I have the stock rear brakes on the several GTRs that I ride and can lock the rear on even the best of pavement.
I realize that newer bikes have disc brakes front and rear, but the disc is not self energizing and are more linear in response to applied pressure. Even at that, with my GS1100ES Suzuki and also my modified GS1100E being much heavier than my 350s the rear brake is used sparingly.
I may have my head "up my butt" and if you feel I do please tell me. My wife does so frequently
DL