You mean has anybody built the camera that HolgaMods copied ? This is the original Holga-gon (Holga with a 90mm Angulon) built long before HolgaMods made it a business. But if you follow their instructions you can end up with a damn fine camera capable of delivering excellent sharp results.
They seem to come and go in terms of availability, there are a few around on eBay at the moment. On top of that you need an M42 mounting flange, and M42 focus helicoid, and an M42 to 40.5 adapter to mount the lens. A Wattameter or similar rangefinder is also good as is a spirit level. All the extra 'bits' between the body and lens add up to the ideal focus distance and coverage for the 90mm Angulon and allow you to nail shots without guessing once you've calibrated the helicoid (the touches of coloured paint in my photo).
I see the 6x12 pinholes, lots of them and fairly cheaply. Am I correct in thinking those will work, albeit potentially with some flange-to-film adjustment?