I have done SBR builds with VZ58 folding stocks and dogleg or stoemwerks top rails.

I did this as a pistol with the Russian bolt on top rail and an ACE folding mechanism with a pistol tube and tail hook.

I am either going to keep as is and add a wood pistol grip,
Or puff front handguard/rails on it.

The Russian mount feels very firm, but I find it suspect. I just don’t believe it will stay rock solid, plus the bolts hang out a quarter in on the other side.

https://photos.app.goo.gl/fqURntJl7YQq3vns1