The SH-6N (formerly known as the SH-7) uses a double thick ceramic, so switching to any regular size bar mag will require thinner spacers.
I put a double thick A8 in an SH-6N but it's still in neck position. A8 sweetened the highs a bit and I think may have made it feel a hair looser, though that might just be my perception. Still pretty big modern sound and feel though.
I also have an old SH-7 Seymourizer which now sports a double thick A5. Haven't decided yet which guitar to try it in so I can't comment on the tone. In bridge position with its original ceramic the pickup was bright, tight and aggressive.