It looks well taken care of. That someone upgraded to a dual brake system is a big mark. If the trunk wheel well is original and not rusted thru in a CT convertible, that suggests the car was always garaged. Look at the passenger floor from underneath. Even garaged, a heater core leak wetting the carpet usually causes a rust thrus. Otherwise, the sheet metal behind the rear wheels usually rusts thru first.
I am sure you have read mixed reviews on drum brakes here. Most claim they don't even work when to factory spec, which is hard to believe. If the brakes can skid all 4 tires evenly, that is the best any brakes could do in normal, sane driving. Of course, you get max braking just before you skid, and if you skid start pumping the brakes. Where disk brakes shine is in faster cooling, which is important in high speed braking (>70 mph) or constant braking (road racing or riding the brakes downhill like FL drivers in NC). My guess is that most people complaining are comparing degraded drum brakes with new disk brakes. A front disk upgrade is good, but hardly an emergency item. Of course, 10" drums are preferred to 9" drums, and most slants got 9" drums.
After rust, next concern is suspension and steering. Look at the rubber bushings at all pivot points of the control arms. Some surface cracks is acceptable, but if the rubber is failing, it will need rebuild. If the ball joint and tie rod end boots are good, the joints should be good also. Turn the steering back and forth and look for play. Look for flexible underhood wiring insulation and that the plastic bulkhead terminals haven't melted.
