Frame measurement needed

[62CHEVYC10]

I am in the process of putting my 62 cab on a 81 3/4 ton chassis. I picked up a long bed chassis and I cut and shortedned it for my short bed 62. The measurement I need is from the rear spring shackle mount on the frame to the rear spring front mount. I need the measurement to be center of bolt head to center of bolt head. I dont need the spring length just the frame mount to frame mount holes were the springs mount in the front and were the shackle bolts on in the rear. My original front mounts for the rear springs were waisted along with the frame were I cut 15" out of it. I built my own front crossmember for the rear springs, just need to know were to put it. Thanks Dennis