Castor Mod Questions

[66 C10 383]

I was reading the Castor Mod thread that chevyrestoguy did and I think someone else also stated there was some type of mod that needed to be done so the top of the coil spring sits in the frame pocket correctly. I've searched and can't find any mention of what needs to be done to the frame pocket. Anyone have pics of what needs to be modified and how?

I'm planning on running the stock 66 crossmember with 73-87 upper and lower a-arms. While rebuilding the front suspension I'd like to do this mod while everything is apart. I'm planning on the Energy Suspension control arm bushings and moving the arms .75" forward.

I thought if I had these questions I'm probably not the only one. Here's the original write up.

http://67-72chevytrucks.com/vboard/s...d.php?t=501241

Thanks