Front Disk Brake ?

[70GMCer]

I'm going to start getting all the parts ready for the swap to front disk brakes. I have a 72 setup with 5 lug rotors, but want to stay with the 6 lug rotors. I see where GMC Pauls sells the 6 lug rotors, but I thought I remember a thread on here a while back about buying 6 lug rotors from a newer truck, and would cheaper. If that's right, anyone have the year truck I need to ask for? Also, is all I have to do on the 70 control arms to accept the disk spindles, is to change out the lower ball joint? I plan on using all the other 72 parts for this change.