Grafting clip - caster and ride height?

[rsb5772]

I'm about ready to graft a '73 Nova clip to my '57 and I'm not sure about the caster. I know I need to level the frame front to back, and side to side, and know about finding the axle centerline, but how do I position the clip front to back to set the caster correctly? Also, I plan on bagging the truck, so where should I position the front axles vertically? I've been told to set them at the same position as the original axle, then install the bag set-up, and if it's not sitting as low as I wanted, then install drop spindles.

Any tips on doing the install would be greatly appreiciated! I've searched it to death and I'm pretty confident on doing this for the first time, just unsure about the above.