We simplified the brake, using a single disc brake rather than dual band brakes.  We also welded our own pedal.  The disc brake we purchased came with a bracket to be welded on to the frame:
We welded an additional support bar onto the trunion, and the bracket on to the bar:
The brake pedal parts:
Clamped for welding:
A closeup of the spring tab and connection
We welded some 3/16 to the bottom of the bracket, both for support and for a protective skid plate:
The total assembly:
The welded pedal (view of the upside down ATV):