The flattop was made by me several years ago. Light tight and working well with wide lenses. I used the 50mm for a while then switched to the 75mm but never got around to buying the correct finder. 6x9 back is also light tight with new light seals.
This looks really interesting. Can I infer that by "flat top" you mean you removed the top (ie. viewfinder and rangefinder assembly) from a Mamiya Universal to create a smaller/lighter scale focussing camera? Did you just cut the top off the universal and add some kind of flat plate (wood, metal or plastic) to the top? Will only a version with a G adapter work?