I installed the dual chamber master cylinder, Only problems I've had is the fact the PO put silicone brake fluid in the system, all components were new when he did this. I didn't want to have to replace everything again so, I stuck with silicone fluid, I hate it, soft pedal etc. Other than the silicone fluid issue, I had a semi-firm pedal at about 4" travel. I startd researching and found with drum brakes, I needed 10 psi check valves, this info was from the streetrod guys. I installed the check valves and don't see much difference. I do have brakes and they work ok, but, I still have a long pedal travel to engage. They don't need bled, I've bled them several times and they don't pump up as if there was air in the system. I've adjusted and readjusted all of the shoes, they are where they are supposed to be. I've sanded the shoes and drums to break any glaze, still have the same results. People tell me that I don't need discs with the stock engine but, I'm leaning toward them, just to get a better pedal feel an sense of safety. If I go to discs, I'll replace the hoses and all of the seals and master cylinder and flush all the hard lines and go back to DOT4. Big PIA. Wish there was somebody around this area to compare notes with. I need someone else with an M37 in the Cincy/Dayton area to get a feel for their brake pedal. I drove these when I and they were in service and don't remember the brakes being like this.
