Not sure why you would want to run a Convertible? My '69 Coronet Convertible weighs quite a bit more than my '69 Coronet Hardtop.
My convertible was built for crusing, but with a mild 505" engine and 5-speed manual trans, it runs in the 13's pretty easy on 255x60x15" BFG Radial TAs (hard street tires), at altitude here in mile high Denver/Bandimere.
I think the car is well over 4,000 pounds without driver.