Back to the slamming door issue:
I put new strikers and door latches on my '62 c-10 last year. I think that if you have original parts still in place, you need to do that first. Secondly, after new latches and strikers are installed, there should be no slamming at all, if you have the strikers adjusted right. It will either catch the striker, or it won't, at least that's what I learned. One of the things I encountered was interference from the inside rubber insulation, as well as a rusted door sill, both of which put pressure on the the inside of the door and caused door slamming. Keep on slamming those doors and you will begin to loosen rear view mirrors and spotlights and window runners, so you have to fix it.
