Can't say I regret the passing of that Kirby-Lauson, but a one-piece deck SB45 seems like a better starting point for a project than a twin rail, especially when the twin rail has serious rail problems. Note that the one-piece deck bolts to the side plates, whereas the twin rails are welded to the side plates, so you can't mix and match pieces of the frame. I don't know why you'd want to anyway, when the one-piece deck frame is a better design.
