Frankenduster, Consider that a 40 + year old car, especially a convertible, is sagging a little from normal use ( not to mention if it's ever been tapped/bumped in the past ) chances are that a bit of sagging should be expected. That being said, I would "unload" the body on the lift and check door to fender gaps as well as door to quarter alignment and ease of open and closing. You may help the car regain its "as new" geometry when installing sub frame connectors.
Just a thought.
Copper