My current MG is a 629 and it has all the features listed and is a joy to pack. The very first MG I had was 29-8 (blued) with the 4 screw frame.
I have heard that the frame were left overs from a 'classic' run about the same time.
I never warmed up to it and one thing that stood out was it DIDN'T have the black powder beveled cylinder like my 629 does.