[vin63]

If I work on a chassis with existing frame rails and shock mounts, I usually set up the chassis with the rearend housing at ride height and measure the distance between the upper and lower shock mounts. This gives me the shock length at mid-travel. Depending on how much shock travel you want (it's a good idea to make sure the length of suspension travel you want for the vehicle does not bottom out the shock you choose), find a shock that's mid-travel is the same (or very close) to your measurement (most shocks will have a fully extended and collapsed lenth spec, or some will have travel length measurements listed). The coil over spring length will be determined by the shock you end up running (some shocks recommend a 12" length spring, others 14" length, etc.).