[Eman]

Drum brakes actually hold better then disc, drum brakes are self energizing. Basically as the primary shoe touches the drum and the drum tries to rotate it this in turn forces the secondary shoe harder against the drum.
To increase brake holding power increase wheel cylinder diameter and install all secondary shoes for more friction surface area. If possible find a larger size shoe/drum setup from a larger car that will fit your rear. raise the pedal pushrod to increase pedal ratio.
Every Fox body I've fooled with has marginal brakes at best.