I did it. There was no helping for the lack of the adapatablity to the Sa mount. So I bought a Mamiya 645 to Pentax K adapter. Pentax K and sigma share a same mount in regards to manual glass. The only difference is the film plane registration distance. But this just means it focuses slightly past infinity and doesn't focus as close as it could. Since we are starting at the basepoint of the Sdqh which is already ornery system to work with I figured why not make the experience even more difficult and manual focus with a dumb adapter and very old glass. But if life exist in balance it paid off with this combo. As difficult as it is, it makes beautiful images in droves.
It really is a big funky setup, but it's like Jazz, you kinda hate it at first and it doesn't make sense but once you get to the finale it makes perfect beautiful sense.
I mainly shoot in B&W on the Sdqh just for the ease of focus when paired with peaking and focus magnification. Sometimes I change the color profile in Sigma photo pro but I really like the monochrome. Especially as older lenses are prone to chromatic aberration. The Foveon is especially punishing but provides beautiful results when you nail everything.
This was just some basic testing to see if the concept works. No scientific data or mumbo jumbo. That's not what I'm about. The only issue is the focus to infinity. It focuses slightly past. No big deal.