I have used Randolf, Sig and Brodak interchangeably, even using all three on one plane, without issues. I believe Brodak comes from Randolf, and Sig may be manufactured by Randolf too--not sure on that one. You can do a test first if you have any worries.

I've never used Brodak's white primer. If you're using Sig red you definitely want a nice base, because Sig red is almost like a dye--it doesn't cover well by itself at all. I agree it looks good if it's done right.

If the Brodak primer gives a good opaque white you should be fine, but I would email Brodak with this question--it's a family business and I have gotten prompt answers from them before.

If you have some plastic trimmings from the parts, I would test the Brodak primer on them. Lots of old Sig kits had plastic parts that you could dope directly, but plastic can be many things, so test it.

Jim