Some background.
Gil Ayan used to post in Ampage and in the Boogie Talk mail list. I think a couple of the Mesa Boogie schematics that are on the net were contributed by him.
From what I remember, the S&S was not a proper "business", it was more like someone at the boogie list would e-mail him and ask, Gil, please build one of those things for me, and he would do it in his spare time. So problably the different caps are because that's what was laying around.
The S&S is not gooped and while he never published the schematic, he never hid that the slim feature was just a series cap for bass cut and the "smooth" was just like a guitar tone knob turned down, and encouraged people to try different caps that sounded best with their guitar, amp and style.
Here's a schematic he published with mods to the Mark I boogie:
http://www.blueguitar.org/new/schem/mesa/
When he published this, he said to look at the input cap mod to learn what the slim part of the S&S was.
http://www.blueguitar.org/new/schem/mes ... _mod_1.jpg
BTW the idea of cutting bass to help keeping the bottom end of amps tighter is not new, many many people used treble boosters for that. But since Mesa amps have more gain than fender blackface amps, I think Gil realized that just shaping the bass was enough, the extra gain of a treble booster would be too much in that case. For a Fender I'd rather use some simple treble booster.