What's the difference between the M type and S type calipers?
 

I am on the hunt for some detailed technical data an numbers. I have a set of after-market front calipers with a mounting bracket machined to fit the 3.5" strut I believe this is the same as the S type caliper. If I was to have new brackets made so the calipers would fit the early 3" set-up, would it be enough to copy the mounting blocks and alter the pitch from 3.5" to 3" or are there other differences as well like offset etc?

Thankful for any advice and details...