i'm not one for advertising for other boards but try
www.cudaworld.com they have 3-70 converts and 2 71's for sale. the sad thing is the 71's are very,very nice but very,very expensive,100g+. i too have been looking for one for awhile now. i have my aar but i want a vert. instead. last feb i drove to detroit,mi from danville,va to buy one that was supossedly a very nice driver that only needed a minor cosmetic resto at best. needless to say it was grossly misrepresented.
to start with the pictures that he sent me where old and alot of parts where now missing off of the car that where on it in the pic's. he blatantly lied about the rust that was in the car and about the running condition also. 30'g + for a car that needed a total resto along with needing a cowl, lower fenders,inner fenders, floor pans,trunk pan, qtrs and missing parts just didnt sit well with me so i left it there.
so be very careful when looking at these cars. pay close attention to the cowl area ,esp to the seam that runs from side to side that ties the top part of the cowl to the firewall its about 4 inch's from the top edge also look around the master cyl. area and look at the hood hinge area. then look under the fenders back toward the firewall area, people like to undercoat them there because they rust out, check for weak spots or patchs there. open the doors and look at the door hinge pillar, if you see bubbles or rust there watch out its bad,,,
also the trunk area around the convert top frame is another place to look closely at.
another thing is to look for the tourqe box's in front of the rear spring perch, if they are not there then look out, it's probably a hardtop car thats been cloned into a cenvert. also check the door glass to make sure that it goes all the way up and seals against the top and the rear qtr. glass, convertible frt door glass is different than a regular cuda. hopefully this will help you get a better idea areas to look at when you find a convertible that you are interested in.