I just installed one of those cheap china disk brake conversions on my 71 Demon. It was a small bolt pattern 14" wheel setup. Are those the spindles you need? Do you have a pic of the caliper bracket in your kit and the spacing measurement? It would help to determine what you need.
The SSBC instructions do not have any measurements. I will go with the larger spindles, so I can mount 14" wheels on the front. I'll 14s in the back, too.