We used the 15 inch alloys that were on the w126 car (88 420SEL). I am not sure the proper term for that style of wheel.

We ended up using the master cylinder from an 82 SD parts car that I had stashed from years ago and a power booster from a 79 300D that I guess I am turning into a parts car now, unless I can figure out how to transplant the m/c and booster from the 420 sel.
I really don't think the m/c swap is possible... unless we transfer all the anti-lock equiptment .
The booster from the w126 (420sel) has the bolt pattern different for the w123 master cylinder.

The hardware up front such as backing plates, calipers and rotors fit perfect though, and was so easy I would do it again on my 80 TD wagon when I wear out all the 14" tires around here.
I don't think it is possible to swap the m/c or booster setup from a second gen w126 car to a w123 car. I was kinda desperate for a booster and really wanted to use the dual pod setup so I looked at it fairly close but I could be wrong. I stopped short of removing those parts cause I don't think it will work, but would love to hear from anyone that might have succeeded at it and how it was done. I know of a few people on here that talked about doing it but I don't think anyone has swapped the antilock equiptment.?