I'm reaching back to try to remember some of this stuff...
I've been riding BMWs since 1990, and my first BMW bike was a 1978 R80. For a time, we had a '57 R69 that was converted using an R75/5 engine (and a Bates solo saddle mounted on old Triumph seat springs for my vertically challenged ex-wife). Lots of other "after-market" or /5 parts as well. We had the small Wixom Ranger bags (similar to yours) mounted on that bike (sorry, attached pic is low-res). Most of these aftermarket mounting options for the old "/2" models (plunger shock models - pre-1970 back to about 1955) required cutting the ball off the rear shock preload lever (which is why finding them with the ball intact is so hard).
The bags you have pictured seem to be for these older models with a FIXED upper rear shock mount (i.e the top shock mount is a STUD that mounts to the bike, the bottom is the standard rubber mounted eyelet). [Note: if anyone still has one of these old-style shocks that needs a spring compressor to disassemble, contact me, as I have the compressor tool, happy to part with it] The later models (including your /6) had the rubber-mounted eyelets at BOTH ends of the rear shock. So the bottom line is that you may very well have issues in getting the old style bags to fit the newer /6 bike (because there is no "shock tower" to bolt up to). I have NEVER seen the "ring" muffler mounts you show, as stock BMW mufflers from that era are "megaphones" (i.e. tapered) and those rings would either crush or slip off those mufflers (maybe they're for the shock tower?). I think more typical is to tie in to the rear passenger peg/muffler mount bolt. (And yes, my old 57 R69 *DID* have straight muffler pipes... these were a low-budget, limited edition aftermarket solution to expensive BMW replacement mufflers, manufactured in WI from copper water pipe and chrome plated, before BMW started making them from stainless steel).
If you wanted to go with the "period" aftermarket touring equipment in use for your /6 bike, most used the quadrilateral "Krauser bags" (possibly sold by BMW back in the day with BMW mounts?). A company called "Reynolds" used to make a variety of sturdy mounts to fit these and the later (/7) BMW "rectangular" bags (along with luggage racks, some even "folding" to access the under-seat storage if you had the "S model" seat with the hard cowling). Here's
a link to a mother-lode of info on them - and you can still find them today on Ebay (Reynolds is long out of business, but the catalogs will tell you what part numbers fit your bike). Note that if you go with the "Krauser" bags, be sure to rig up a strap w/buckle as additional security to hold them in place (and ones with keys for the latches are a good idea, as many keys get "separated" from the bags over the years)... the single latch holding the bags in place had a reputation for sometimes "ejecting" the bag from the mount when a bump was hit. Here's
a link to a /6 with the Krauser bags...
So I'm not saying you*can't* find a way to mount those bags... but I suspect it will surely be a challenge and you may need to fabricate your own parts - it seems you're trying to mix parts from 2 different eras. The /6 was a very reliable touring bike. If that's your plan, go with the Reynolds/Krauser combo, well proven over the years.
