The polaroid/Graflex back is to use Polaroid roll film on the Graflex, not to convert it to 4X5. This film has been discontinued many years ago.
If you're going to pursue this you're going to need a 4X5 back to add to the 110. What you're doiing right now is converting from a roll film back, to a roll film Polaroid back ie they both use the same film. With the added 4CM extension you'll have a close focusing camera with no film available for it.