Slick 60's

what is the oldest crown vic you can get a good crossmenber out of for a 65 f100

Good as in "unbolts" is the aluminum setup found under '03 and up Panthers, ie, CV's, Grand Marquis ( especially the limited production "DeSade Edition" ) ,Marauders, and Lincoln Town Cars. Various component changes, including materials, were made on an irregular basis until the end of production.
Earlier Panthers are good candidates for full-frame swaps or front suspension grafting.
Paul