I finally made my choice for a Cambo in mint condition, since the cheaper Toyo was in bad shape.

So here are the Cambo measurements if somebody is interested :

The frame is externally 162 mm, corners are round with a radius of about 10 mm
The internal opening is 117 mm, there's a lip of 1.5 around it (1mm height) so that the frame's lip will fit in a 120 mm opening.
Around the lip is a rabbet of 4 mm by 2mm depth.

I also bought a very cheap Sinar in bad shape (but still usable) that will make a hood.
The dimensions are :

Frame external dimension is 139.5 mm, internal opening is 120 mm.
There is no lip, but a light trap of 135 mm external, 128 internal, and 2mm depth. Radius of the external part of the trap is about 2mm.
The bellows could be held by an external rabbet, which is 3mm thick and 2.5 depth.

In this aspect, the Cambo is the easiest since it has a wide frame around the bellows, which makes attachment easy.