I have been all over my manuals and this site and have been unable to find a torque spec for the Leaf spring centering bolt on a 64 1/2-65 K-code vert.
Me too. In this case, I looked at the spring specs, and general specifications in the suspension section of the 65 and 66 service manuals; the AMK Guide to Ford Fasteners; and the 69 Standard and Utility Parts book. No grade is specified, so you fall back on the general guidelines for hardware torque, which is, for a 5/16-24 threaded bolt,
12 foot-pounds. A grade 5 bolt is 19 foot pounds and I would recommend that you not go past that.
I believe that Ford serviced the rear leaf springs as a complete assembly, so no torque is listed.
Jim