Make Your Own
Interested in compact outdoor wide angle? Low budget? This the one for you.  I obtained a good Universal body with broken (dropped and useless) rangefinder & viewfinder and modified it to become a great wide angle delight. 

Standard 23 Nicer Look Body
Although I used the Universal body with my first Flat Top, the Standard body is much more attractive as it is a nice square box. Additionally, is is a little easier to work as it has fewer through holes in the top of the casting in the casting to plug after milling off the top. The only major difference in the two is the lens mount arrangement. With the Standard the lens is twisted into the mount. With the Universal the big ring on the body is rotated to attach the lens. Since we are doing away with all the useless viewfinder and rangefinder stuff anyway the mounting system is not important.  

The 50mm and 75mm Mamiya lenses don't have notches for the Standard lens mount latch but the notch is easily cut in with a Dremel tool with 5/32 cylindrical rock. The Universal doesn't use a latch.

Here's How:
Removed all rangefinder parts, screws and hardware. What you can't remove will be milled off, no problem. The surface to be milled down to (limit) will be apparent when you take the parts off the body. You need to give exact instructions to the Bridgeport operator. He will "kiss" the surface with the tool. This is a very simple milling job for any shop with a Bridgeport type milling machine. Their minimum setup charge will usually apply. My shop charges me $45.00 minimum.
Clear the through holes and plug with set screws, glue and black paper top and bottom, cork , rubber, etc to seal holes to seal out mother nature's light. Use flat black paint stuff from Micro-Tools to seal everything.

Cut, shape and finish a 1/16" aluminum cover. The aluminum can be found in all good hardware stores and cut with hacksaw. Use soft jaws or cardboard in the vice. Clamp the finished cover in exact position and drill four #43 (4-40 tap drill) holes in the cover and down through the top of the body. Holes should be close to the edge and avoid existing holes in the body. Position where ever convenient. Tap the body holes #4-40 and counter sink the cover holes. 

With a Graflex roll holder on this body with the top lowered 1 3/4" inches or so, the finder must be mounted slightly to the rear so one can get an eye to it. If used with Mamiya roll film holder this may not be necessary and you can mount shoe at rear of cover.

Cut and dress a 1/8" x 3/4" x 1 1/2" aluminum bar. Mount the shoe square 1/16" from the rear end of the bar. (Really square.) Mount the bar square (Really square.) to the aluminum cover with 3 or 4 #4-40 flat head machine screws.  Check drill and nut clearance.

Keep Viewfinder on the Camera
For viewfinder safety, to keep it from falling off, attach Velcro pile in front of the shoe mount (see pictures) and cut and fit a Velcro harness to loop around the viewfinder and attach to the pile. This harness is very important even if you use the type of finder with the screw lock. Just a small bump can catapult the finder right off of the shoe.                                                 Click Larger >>>

Finders
Mamiya has made some fine finders for the 6x9 and 6x7 formats: 50mm with screw lock, 65mm Gray offset mount for Standard, 65mm Black center mount for Universal and Super, 75mm with screw lock and additional frame for Polaroid format. The Koni or Rapid Omega finder for the 58mm-60mm lens and 6x7 format is fine for the 75mm Mamiya lens and 6x9 format. It has no locking mechanism, so the Velcro harness is handy. Rubber bands can be used also.

The handle on the right side is optional. I use my Flat Top on the tripod and seldom use the left grip. 

I use this hybrid with the 65mm Mamiya and a Koni-Omega 60mm finder and the 50mm Mamiya with matching finder. With a couple of the Horseman true 6x9 or 2 1/4" x 3 1/4" roll film holders this camera and either lens arrangement makes a great wide angle outfit. Unlike the Graflex XLS and XLSW with Graflex lens arrangements, the Mamiya lenses have good distance and and hyperfocal scales.

To tell the truth I like the less expensive 65mm arrangement best even though it is older and inconvenient to operate with a proper lens hood in place. The 50mm on the 2 1/4" x 3 1/4" Horseman format is serious wide, about 80 degrees of view. The 75mm Mamiya is a later lens with a circle of coverage large enough to cover the 4x5 or 6x12 format. See: Mamiya 4x5x6x12 Ultrawide.