Santino,
Can you post some pictures of the rear-standard of your camera, and the focusing screens ?
Assuming you have a non-American version of this outfit ?
If it does not have a "spring back" like a wooden view camera or a Speed Graphic press camera, it probably has an "international back", similar to European folding plate cameras circa 1900-1950's.
These have "tracks" on three sides of the back-frame, and the focusing-screen slides-in and locks in place for focusing on the Ground-Glass, then when the camera is set, the focusing screen is carefully removed, and a film or plate-holder, or roll-film adapter slipped-into place, dark-slide pulled, and exposure taken, etc.
IF this is the case with your Peco, Plaubel-RADA did make a roll-film adapter for 9x12cm "International" back that uses 120 roll-film, and can make 6x9, 6x6, and 6x4,5 cm images, provided the adapter has its appropriate masks.
Otherwise, you would need to find 9x12 film holders, or plate-holders with film adapters, AND 9x12 sheet film (FOMA ?) or cut-down 4x5 inch sheet film.
I use the RADA 9x12 > 120 adapter on a 1920's Zeiss folding plate camera with decent results.
I hope this is of some help...
Good luck !
Luddite Frank