Re-install the original wires per pictures from original post, if the snare disengages properly you have found your problem. You can also check that the Gibralter wires are not installed upside down. On the original Slingerland set where the wires are physically attached to the plates should face away from the head. Or, perhaps more clearly stated, the flush/flatter side of the snare wire assembly should face the head.

Great tips here. Thanks all !! Just received period correct heads and a Zoomatic with a knob for mine. Pop out some dents and should be good to go. Can't recall which snare but one liked the snare wires a bit toward the butt side as opposed to centered at tension to fully release. Could be the reverse here. You will get it going and be very happy with the results.

Creighton