I'm an avid fan of Yashica cameras over here in the United States. I'm particularly fond of the J-series SLR cameras of the 1960s. I wanted to share some information with you regarding a Yashica-made camera of the mid-1960s that you might find interesting or useful.
I recently purchased a Wards SLR 600 camera and lens from a thrift store here in the US. The camera is in excellent condition and I'm currently running a roll of film through it. The camera also came with its original owner's manual and the original Tomioka-branded f/2 lens.
After buying the camera I started doing a bit of research on it to try to find out more about it. I could tell right away that it was made by Yashica, but also could see that it wasn't a direct rebadge of any Yashica-branded camera. I also noticed that you mention this camera on your website.
After looking into it a bit more, and looking at the details of the camera I now own, I've been able to piece together some information that you might find interesting:
1. As you note on your website, the camera appears to be an amalgam of different parts from Yashica:
a. The self-timer lever and underlying mechanism are from the J-3
b. The film advance lever and frame counter are from the J-3
c. The shutter speed dial is the later style of the two J-3 styles (the one with green numbers 60 and above, and the "X" next to the 60)
d. The rewind knob is the J-4/J-7 style
e. The nameplate area above the lens is the taller embossed valence style of the J-4/J-7
f. The light meter is the J-4/J-7 style and has the white meter readout of the J-4; however, it lacks the battery test button of the J-4/J-7
2. The lens is a semi-automatic aperture type, and the aperture trigger mechanism in the camera is the single-movement type that only supports semi-automatic apertures.
3. I researched old Montgomery Ward catalogs and found the following:
a. The camera was first advertised in the 1964 Fall/Winter catalog. In that catalog it states that the SLR 600 would be available to order after August 1st. It also states that the light meter features a hi/low range selector, and the image of the camera clearly shows a J-3 style light meter/rewind knob assembly on the left side of the camera. The image is also clearly a doctored picture of a J-3, with the "Yashica" brand simply covered up with a rather crude rendition of "SLR 600".
b. The camera then next appears in the 1965 Spring/Summer catalog, and in that catalog the description of the camera no longer includes the hi/low light meter range, and the picture of the camera looks like the camera that I own, with the J-4 style rewind knob and light meter.
c. The last time the camera appears in a MW catalog is in 1968.
d. One interesting thing is that the 1964 catalog lists two additional TOMINON lenses available for the SLR 600: a 135mm f/2.8 and a 35mm f/2.8. The 1965 catalog lists two additional NICCA lenses available for the SLR 600: also a 135mm f/2.8 and a 35mm f/2.8. All lenses are listed as pre-set lenses.