if it's fixed it may be sized to the M/C. are you running the same size tires (front/rear) as the Fairmont?
No, the tires are not the same but the rims are. 14". The Fairmont is a 6cyl with power brakes, the maverick is 6cyl manual disc brakes
When we did the manual drum to disc swap on our 65 Falcon, we used this one... http://www.jegs.com/i/JEGS+Performance+Products/555/63020/10002/-1 it should work with drums or discs. After installing, open it all the way up to bleed, then adjust the rear + till the back locks up easily, then adjust back down 1/4 of a turn til it feels right. Definitely worth $40
Either use a late-model Maverick proportioning valve or get an aftermarket one that is adjustable. Either way, you'll have to change the size of the brake line fittings.
Pic posting problem gone. Here's the valve we got and you can see the dual chamber master behind it (painted red to match engine)