Bump for this, I am interested also as a K5 will be my next project, I found one running for $500. It's a little rough, but I am decent with body work and paint...Good Luck with yours, they are fun, old trucks

 

K5 with the full convertible top? If that's the case...low back baja seats are the only way to go. Newer seats are too tall in my opinion.

Check out summit or jeg's, they're reasonably cheap seats.