The outer discs are interchangeable from side to side- doesn't matter which side they go on. It looks like the calipers are out of adjustment to me. When you push the sticks forward the arm on the caliper should push backwards and stop the inner disc. The adjustment for the inner disc pad is an allen screw on the back side of the caliper. The other adjuster is for the brake disc.
One other thing you may want to change: The RPM is too high to change gears. The straight-cut cogs in the reversing unit will round off if they keep grinding and eventually the trans will pop out of gear by itself. the input pulley should be stopped or nearly stopped when you change gears.
Hope this helps.
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far