Hi,
Same in the front as the rear? I’d suggest using simple geometrics & the level floor in the picture to locate the issue.. You can do some or all of the steps, think you’ll understand, please ask if unclear.
Verify sheet metal gaps as uniform, not locked tight on one side, opposite the other & heights are the same.
Measure 4-6 points from the floors edge,(front & right) strike an inverted & mirrored ‘L’ line between them so you can drive squarely up perpendicularly.
Jack it up on that nice flat floor & place stands on the same areas opposite one another on the frame, letting the
Suspension drop. If the floor’s true, stands same height, jacked on similar points, car reads level..your frame is likely fine.
Suspension hanging level?
Take/record some measurements, use your (2) lines as reference dimensions & use a straightedge to draw small lines under the car on each side at spots you want to measure from (so they’re the same points on each side). Pull the tires & measure floor to unitized frame &
suspension pivot points at several different intersections, cross corner & see if the sides match. A twist should show up pretty evidently.
Car still on stands, centralize a Jack under the differential & see where it begins to lift the body (don’t need to actually raise the body off the stands) into the load bearing support of the coils, should see the axle kick up on the side with the weak spring as you go higher up, deflected by the stronger spring.
It’s not a frame rack nor Tram gauges, but will prove the origin of your issue.
Good luck!
-John