The RCMP advised me, in writing, to register is as an SAS-3 sten receiver and requested a formal submission of my design on paper. If it gets approved, they will issue a brand new FRT number and permit me to complete the build.
And I would not recommend anyone bring an SAS-3 receiver to the range with a non-SAS-3 firing mechanism. Maybe you would be OK, maybe not. I wouldn't risk it PERSONALLY.
As of 3 weeks ago when I spoke personally with George Fraser at the CFO, there were no approved FRT numbers for open-bolt guns, only closed-bolt stens. As I stated many times, I would give a left nut to know what FRT and FIN these "approved" open-bolt stens use as the maker has repeatdly refused to offer comment - so much so he was banned for probable illegal activity.
'nuff said.