I recently acquired this off of the local CL. It's a custom built bike from the 80s by a guy from Washington state. I don't know much/anything about the builder, other than he built about 15 Tandem bikes during that period.
I did find pictures of a 650B tandem that he built, while searching for more info.

Last year I bought a Jack Taylor tandem to ride with my kids and wife. it fit my daughter and wife real good in the stoker position, but was a bunch too small for me. I did make due and put about 250-300 miles on it, but the saddle to bar drop was too much for me(with a lot of seat post showing). Regardless, it was a nice riding bike.

Anyhow, I found this bike, and the size is better suited for me, and the same size as the Taylor bike in the back. Since picking it up, I've only had to clean it up a little, and service it. The hydraulic brakes are new to me. I like the feel of them, and they seem to slow the beast down real good. However, I will be looking for the parts and tools to do a proper bleed on them and get them set up correctly.The rear derailleur might get changed out, unless a hanger alignment cures the noise and shifting woes that I'm having now. I did remove the old Campagnolo dt shifters for the Simplex parts that are on it now.

I've only put about 25 miles on it with my Daughter, but I can say it is much more comfortable for me, and rides at least as nice as the JT did. FWIW, this bike is about three inches longer than the JT. This looks to be a pretty well built frame, and slightly out of the norm. I've never seen a bike with an oval top tube to match the beam on the bottom.

The parts list:

Frame: unknown steel - 61cm f/49cm r

Phil Wood hubs/Super Champion 48h 27inch rims
Specialized crankset
Shimano Deerhaed rd
105 fd
Simplex Retrofriction shifters
Magura hydraulic rim brakes
Brooks Professional saddles
Blackburn rack
Bars: Controltech f/Specialized r
Stems: Modolo f/ System 2 r