My fave nub for a lightweight frame was how we did 'em at R+E around '79-'80. Glenn Erickson's idea.
He took a Bluemels fender stay out of the trash, filed the end smooth. Brazed a tiny dot of silver on the end, then while still hot pressed that end against the frame and heated just until the silver re-melted. Snipped the rest of the fender stay off with a small bolt-cutter, and filed the cut smooth so the remaining bit was maybe 1.5 mm tall, shaped like a hockey puck. Almost invisible but plenty to keep the clamp from sliding. We brazed them off-center so they wouldn't hit the gap in the clamp where it pinches shut. Absolute minimum amount of weight added (hah!) but more importantly, the minimum of heat-damage to the 531. Which could be an issue depending on where you cut the miters, this might be on the thin unbutted part of the tube. Still pretty theoretical, but why not optimize?

Best part was it took something like one minute, probably less. We got dozens of frames out of that one fender stay until it was too short to hold with your fingers for brazing.
Framebuilding in the stone age...

Another favorite of mine, for keeping the clamp from sliding:



That sucka ain't goin' nowhere.

Oh and This Moto Team Champ method takes more heat, but the payoff is the eye-candy: