03 crown vic track width will be too wide prolly, eh? (67")
check the inside fender width from inside lip to inside lip on your truck, then compare that to a crown vic or other donor. if you get the parts for free some extra work seems like it is bearable. I have seen builds where they put the truck on the complete crown vic frame, Fords though usually but that's just the name plate.
check this build thread, starting on post 104. he has widened the rear fenders to match the track width he has after a corvette suspension was installed with wide wheels. awesome job. crown vic could work if you do a little fender fab work after. looks like your fenders will need some help anyway.
https://67-72chevytrucks.com/vboard/...=766016&page=5
crown vic stripped frame
https://www.idmsvcs.com/2vmod/hybrids/ladderframe2.jpg
thread with crown vic frame dimension drawings
https://www.ford-trucks.com/forums/1...r-81-f150.html