I was missing my original bench seat for my 59 Chevy. I was able to locate a 56 GMC bench seat and reupholstered the seat. Look grate. I thank the answer to your question is second series 55 through 59 Chevy and GMC’s will be interchangeable. If you need to locate one I have an extra bench seat that needs to be reupholstered. I did mine for the first time and looks grate. The upholstering kit is around 250.00. Steve slang9459@aol.com
