I did this over 20 years ago to my 750ss and have never looked back. You can get away with the smaller, single disc m/c but the upshot of all that is that you end up with a lot of lever travel, which is less than ideal. I even did a trackday with the lesser master cylinder, without issue, but the proper one is better. You won't be able to do the 4 pad caliper upgrade without some adapter plates for the fork bottoms, because you should have 40mm spacing between caliper bolts, and the later calipers are 65mm spacing. There seem to be more early white frame and wheels SSs coming out of the woodwork these days. I've owned two of them, the first one VIN ***0132 was stolen form my flat in High Wycombe over 20 years ago. The other I still have, but it only gets out occasionally these days. I'm looking to change that this year.
Doh, I was getting my 4 pad calipers and 4 piston calipers mixed up. All the front Brembos are 4 piston, but only the later ones are 4 pad!