You can focus in two ways: 1. Set the front cell to infinity and focus with the Polaroid mechanism or 2. Set the Polaroid mechanism to infinity and focus with the front cell.
I really like the Polaroid mechanism and have drawn up plans for a slightly enlarged version fo a hand held 5" x 4" camera. Unfortunately it's just one of three million and seven crazy ideas I have and I only get round to trying out a few of them.
The lens is 105mm (I think) from a Zeiss folder which had seen better days as far as the bellows was concerned. It started with a Kodak 110mm lens and some extra spacers but the Zeiss lens was a better fit.
There is a link at the bottom of my post to a 6x12 camera which is very nearly complete.