Fisher Body manual has a long and detailed adjustment/setup procedure in it for window alignment. If you follow the procedure, and if your car is straight, they can be improved.

The reason they're difficult to go up and down is likely because the 43 year old grease in the tracks, regulators, and guide wheels has changed into a solid/hard wax due to age. So before attempting any adjustment remove ALL the grease from the window mechanisms and re-grease them fresh...they'll probably work like butter.

Convertibles have a factory cross brace that is often missing...6 bolts on a good sized piece of sheetmetal that bridges the driveshaft tunnel under the car. Is yours there and installed tight with 6 bolts? That's the only extra support from the factory. It helps a little, but they're still very flexy even with that in place. And how old are your body mount bushings between subframe and body? If original, they're junk. Replacing them often improves flex, and often leads to a subframe-off restoration after you realize the cage-nuts are spinning and you can't get the bolts out, or the holes to install them in the subframe are rusted out oversized and can't even accept the new bushings. Almost 100% of rust-belt first gens have this problem, and it creates a ton of body flex and impacts body panel alignment and drivability.

The normal solution for convertible body flex on these cars is to replace the body bushings (original, poly, and solid aluminum are available) and then install subframe connectors. What type of bushings/connectors and how to go about the project depends on whether originality is a concern for you or not, and how much $$ you want to spend.

Rust in the chassis is the other huge cause of body flex. What kind of condition is your car in from a structural standpoint?