Wishbone setup help!?!???

[charx2]

I am really wanting to get this setup...http://*******************/4-link-kit...t-wishbone-kit
Problem is, it says I need to measure and figure out my lengths but I'm not sure about what lengths I need. Can someone help me figure out what I'm measuring for? I do know I need to measure for my lower lengths and I think the spread, I'm not to sure though? It's going on a 67 C10 with a 12 bolt, bagged on the trailing arms. I'm going to step notch it and I want to put this wishbone on while I'm notching it but a little worried about not getting the correct sizes. Can anyone help or point me in the right direction? I've done some searching here but nothing really tells me any measurments or even how to measure for them. Any help is appreciated, thanks.