Suspension help needed

[FreakOfNature]

According to the previous owner of my 66, the lower control arms, spindles and brakes on my truck are out of a squarebody, previous owner couldn’t remember what year the parts donor truck was. I’m wanting to put a static drop on the truck to get it lower than it is now. Belltech has a 4/5 kit for the 66 but I don’t know if that would work on the front with all the components being from a squarebody. Could someone tell me what the difference in the control arms and spindles from a 66 and a squarebody are? Can I use the Belltech kit for the 66 or do I need to find a front kit made for a squarebody? Thanks in advance for any info you can give me.