This is the same vintage as my TX750...only I believe this is a 600. Mine had what was called Omni-phase balancing on it (that's why I got it instead of the Norton). There was a counter rotating balancer on the crank shaft that went in the reverse direction as the connecting rods. It was supposed to balance out the vibrations of both pistons moving up at the same time. Worked pretty well too....except it was always jamming the electric start and I wound up kicking it over most of the time. Nice bike...when it ws running.
My father-in-law used to ride a Triumph Thunderbird. He traded that in on a 500 cc Matchless Thumper; and traded that in a Motoguzzi. Eventually sold the Mother Goose and got a Honda 750 Automatic. Last bike he ever owned. That automatic was a taller than average bike and he has really short legs. A couple of times his feet slipped on gravel coming to a stop and he dumped it. He was in his 60s and he saw the light...decided right then and there that it was time to hang it up. He'll be 90 next December.
I remember trying to kick over that Atlas I used to ride. It took me a while to get the hang of the compression release. Every once in a while, if I didn't get it just right, that thing would kick back and about throw me over the handle bars. That and carb tickling...never once rode the thing that I didn't come off it smelling like gasoline.
Wow. Looks like an old Matchless...or a Norton. I used to ride a Norton Atlas 750 back in the early 60s when it was the biggest bike you could find next to a Harley.