That might be better question for Samsquatch (above), he knows more than I do about that frame specifically. FWIW, it seems like a great match for the Progressive spring and a co-worker has that exact vintage Patrol with a Hazzard and Progressive spring, and loves it. Re: spring rate. You want to use a spring calculator like the one on our site to determine that. You don't want to reduce the rate simply because it's progressive. The way we label our springs is by what their closest linear-spring equivalent is around the sag point. So, at around 25-33% of compression...