if you do replace the frame- be sure to get a 2 door frame. the 4 door, station wagon and el camino ones look similar but have a longer wheelbase. It’s possible to cut and weld it to size but more work involved. Fab skills vs time/ money, etc. many posts online about this subject. Also, should you locate a 2 door hardtop frame as mentioned it won’t have the boxed rails which would be more critical for a convertible as it lacks the body structure but there are kits out there to reinforce these frames as the factory convertible ones seem to command a higher price. it might be cheaper to go this route. an example of a reinforcement kit:
https://www.opgi.com/chassis-suspens...r-ch30614.html hope this is helpful