I purchased a vert that had already had the floors repaired. They used the long patches for each side. I think it sucks!!! They were welded in using plug welds around the edges and then sealed so it looks horrible for sure.
I myself am very close to cutting the new pans out and going with a full pan.
I have a friend that has done restorations for 35 years. He tells me it is easier to put in a full pan than to cut out and use the patches. He can by himself do from the firewall to the tail lights in two days.
With a convertible you can get the pan in pretty easy. On some Camaro's with roof he has to split down the tunnel and then butt weld back together. You cannot tell it was cut.
With the convertible the seat platforms and the underside reinforcements of the pans are different so be sure and get the out in as good a shape as you can.
You will need to build you a way to support your body to keep it in alignment. They do sell them already built. If the floors are already really bad the car might need to go on frame machine first to set the frame rails in position.
There are locator holes in the frame you measure from and a great frame jig will save you many many hours of work trying to get everything to fit.
You need to have the ability to have the doors on so you can check before you weld the pan in solid.
Dynacorn is probably the better choice right now. Do not think there is really another out there.
Other member did mention they do not make a pan specific to the convertible. The rocker boxes are different from vert to car with top and flange down the sides is opposite way on vert.
If your floors are gone that is usually the result of leaking cowl allowing water to run into the floor in front and from leaks in the convertible top it rusts out the rear.
I am pretty sure you will need to do the cowl also. I would probably suggest doing floor first then cut the cowl out and replace upper and lower there.
I still feel you are ahead of the game and way less money to look for a great rust free car instead of trying to replace all the panels. Even if there are no holes showing probably 50% of the rocker box is probably rusted away so you loose 50% of the strength. Same with inside the frame rails and such.
The inner front fenders usually rust just behind the shock tower up at the top fender mount.
You also have rust in the torque boxes and the front end of the rocker box below the A posts.
Many builds fail because the task overwhelms the owner and they give up. Any car can be fixed but there is a point that you should not invest the time or money to do so.
Go to the Graverobbers web site. They are near Atlanta Georgia. The do decent work for the money they charge and probably better than any amature can do.
https://www.graverobberssheetmetal.com/index.php/custom-frame-jigs
I guess their price list is disabled it would not come up. You can see what a proper jig looks like in some of their pictures. The firebird they are putting together used just the cowl with the VIN# looks like. That is the way the Camaro's and Firebirds go.
You strip the car down and they take it from there and send back with new panels in primer. DO NOT expect it to be perfect there are no perfect repair panels out there. They do the panel replacement not the perfect body work needed for a show car. You will need to massage the panels on the outside if replaced.
Yes there are people that do the whole job but for a 71 - 73 Mustang you can drop $85,000 to $100,000 for a Concourse restoration and it would be worth maybe $30,000.
I encourage anyone to do their own work but be prepared to work lots of dust, cut fingers, broken spot weld cutters and lots of sweat.