Having recently completed my '58 GMC Suburban, I can relate to you my experience with the GMC (the Chevrolet may be different in minor aspects), and a clamshell tailgate.
Generally, the sheet metal from the doors forward is available from a variety of vendors which I posted some time ago. Aside from the rear seat, the items which are "rare"(except if money is no object), are as follows:
1. Front grille
2. Parking light(chrome plastic) lenses and housings.
3. Tail light housings.
4. Tail gate handle and rod assemblies.
5. License plate light housing and rod assembly.
6. The clam shell metal guides for the retractor cables.
7. Heater core.
8. Clam shell lift arms.
9. Clam shell rear glass.
Luckily, my Burb was fairly complete, I replaced everything I could with NOS parts when possible while restoring and renovating, including all bolts and nuts. The window pulls are readily available, as is the battleship linoleum, but you will have to router the grooves. Also , the hardware to hold the seats to the floor is not reproduced, although a member here was working on reproducing these parts, and another member is planning on selling the grooved linoleum. Rear sheetmetal is not available or interchangeable, but, from previous posts, Ray Stanley can make anything. All weatherstrip and chrome is available.
If I have forgotten anything, I'm sure other members will chime in. It's a fun project and I wish you luck in your endeavor.
Mark.
