If you want to stick with Toneriders (which is what I would if it was my build) the TR website provides more information on their pickup spec than PBG that would be helpful in making a decision.

Looking quickly, I reckon another AC4 Neck would work just fine in the middle. Are you getting covered or open HB's?

It's not that you can't mix brands, but it can present problems getting a good match if you don't know what to look for technically.