These can be converted to take 4x5 sheet film holders (
Razzle does it.
If you don't dismantle everything, put plenty of blue painter's tape on the inside to avoid picking little metal shards off everything...
The mod is done by milling a part of the back and removing the pressure plate door...
For those who don't have a lot of experience, attempting something like that is almost guaranteed to kill the camera.
Take into account the film registration distances or else you won't be able to focus properly...