You are being a bit hard on yourself.
Scale focusing is not that easy with a 100mm lens !!
Measured distance or guestimated?
The images of Eric Salomon that I remember most are usually 10 feet or farther away - much easier to nail scale focus at 10 feet or more!
How easily could a FOKUS rangefinder be mounted on the left side of the camera?
BTW, the number on the back of my Ermanox lens (looking thru the broken open shutter) is 150876
The number on the edge of the shutter crate is 1185538 (partially obscured, not absolutely sure of last two digits)
Apparently Ernemann numbered all camera models consecutively.
Those shots of Joe were taken with a +2 closeup filter (thank you farlymac!) and I focused on his eyes using the ground glass. So perhaps a) Joe moved a bit between the time I exchanged the ground glass for a glass plate film holder, and b) I dim-wittedly had the lens at like f/2.8, of course I knew his entire face wouldn't be in focus, but still went ahead. Ah well.
As far as attaching an auxiliary rangefinder, I've thought about it. I'd have to get some kind of cold shoe with a threaded adapter, but then it might interfere with the neck strap arrangement I currently have going (I've tried attaching the strap on the underside of the camera and I don't like the way it hangs). The FOKOS or FOFER is an option, or I could just hand-hold a FODIS. There are other rangefinder options out there -- I know, despite having spent a small fortune on this camera and its repair, I'm not crazy about spending another $400-$500 on a rangefinder.
Yes your camera is pretty close to mine -- your body is about 700 units newer than mine, both likely 1924 (first year).
I'm getting a nice collection of accessories for the camera -- original case, about 20 glass plate holders, two roll film backs, a couple of lens caps, and a nice selection of Series 7 filters courtesy of our good friend 'farlymac'. Still looking for more glass plate holders, as well as that 'felt' that's used in them for the light-trap. It's mysterious material!