Sorry for the very late reply.
Originally Posted by rshaw
Here's what I did:
1) From the 405 back, I unscrewed one plate on the lens side of the back. Lot's of screws (like a dozen), whole plate comes off, there's a smaller plate underneath that also needs to come unscrewed, and that's it. You have a Polaroid back with a huge openening on the lens side.
2) From the pack film holder, I unhinged the "lid" part and just kept the side that attaches to the camera.
3) Take an aluminum sheet, make an opening for 3x4, attach to the pack film holder part, then drill holes to attach it to the 405 back