1.) The pivot point of the brake shackle on the backing plate or caliper bracket must not be positioned vertically above or in front of the wheel axle (driving direction). In this case the moving forces in your fork parallelogram will be reversed and the fork will rebound instead of being compressed when you apply the brake. This will generate very high forces to impact on your rigid fork leg with possible damage.

2.) Caliper bracket or drum brake backing plate must float on the wheel axle. If not, the fork will rebound as well when applying the brake. Result: see above.

These articles can be used with either DOT4 or DOT5 brake fluid. However, DOT4 and DOT5 must not mixed, due to being chemically not compatible. One should always stay with the same brake fluid type.