Lowering the seat foam

B'cuda said
My brackets don't have that nifty adjustment, maybe because I sourced them from a 69Charger B body? 35 yrs ago I didn't see any difference and they fit my 69 cuda, even recovered the cores with cuda covers

That is correct, your '69 cuda with '69 Charger seats would not have that adjustment.

The OP's '64 Valiant, if it has original bucket seats, should have it.