I think the BOP wagons all have the flap, for whatever reason Malibu’s didn’t. Guess Chevy back then really trying to cut costs and be the cheaper option(?).
I agree. Of the wagons I've seen in the yards, here is the flap score.
Cutlass 0 out of 6 *
Malibu 0 out of 5
Regal 2 for 2
Lemans/bonneville 4 out of 5
* it was available on cutlass, my brougham came one, but its the only one I've seen.
But, even if you find one, chances are the spring hinge is rusted or bent and not salvageable. I've tried to rescue them but were unsuccessful.
If you do find one, its riveted to the cargo bed floor from underneath. You'll either have to take the entire cargo floor or cut the floor out.