Beautiful Sonic Weld BSA Gold Star built by Goldstarfreddie from New Jersey. I lifted the photos from the forum on britbike.com. Reminds me of the stance of the Sideburn Enfield 500.
Sonic Weld style frames are still being offered, brand new, by Cheney Engineering in the USA.
The builder of this bikes says...
This is one of those new Sonic Weld frames using up a lot of my old flat track parts. The cases are B33 with an early GS crank and with the quill timing cover and top breather. It handles like a 250 Bultaco but costs 5 times as much I thought this would be of interest to someone with only a motor as he makes these frames for various motors.