There's a little more to it. Coupe and convertible doors and door glasses are different. You have a pair of coupe doors. They will work on the convertible but you will have to swap out the door glasses with convertible door glasses if you want to run a folding top or the optional hard top on your convertible.
Your convertible half should include the decklid and the decklid springs. These could be added to the coupe body, but it would be less work if they were included with the body half.
68-75 doghouses do not mount quite the same as the one on your '80. If you want to use the 80 doghouse on your convertible, you will need all the assorted '80 bracketry and the inner fender panels.
Original 68-72 fiberglass is press molded and used polyester resin and bonding compound. All the GM body panels on your '80 are SMC. To bond the two types of fiberglass, you will need bonding compound which is compatible with both types.
My advice would be to purchase the 1980 assembly instruction manual (AIM) and the AIM for the year of your convertible donor. Compare the various parts and assembly of the two bodies. You'll get an idea of where you're headed.