77 Mustang II Mach 1?
The radio would be the same for any other Ford of the year.
The gas cap off of a Pinto would work.
For body work, any other Mustang II
I am giving you two links, one for a Mustang II forum. Some one may have parts you can use there. Another for a parts supplier. I am sure there are others.
Any auto glass shopshop should be able to provide the glass.
The exhaust system could be made by a custom exhaust shop, they should also still be in the system if you can wait for them.