if you get under the car, on the side of the tranny is the shift cable, its got a clip that holds the cable tight, they wear out, bend fall out, or even break.
and im not 100% sure on the 69, but when you work the floor shiftier, watch the column closest to the dash it some years it also turns with the PRND21 in the dash. on the fire wall by the brake booster is some rigged up looking linkage, its all part of the shifting, so make sure its all tight as well, its made with rods and cotter pins.
you can turn the column and make the floor shiftier move as well on the years that have this odd deal. if the key ever fails to unlock, or the reverse lights dont come on, this column turning is something to look at always. turn it a bit, the key turns back, or the back up lights come on. its also what locks the floor shiftier.