Hi TYS, can you please post a pic of the pickup wires ? I have a feeling if they are just hot wire and earth they need to be modified to have 4 wires which someone has done a small tutorial a while ago, maybe Scott (Weirdbits).
I think a freeway switch generally has 6 positions so builders with 3 humbuckers use it and still have a toggle style switch.
You will need 1 or 2 x 500k push pull pots depending if you want to be able to control neck and bridge pup on one pot or separate on 2 pots.

If you haven't mucked around with modifying pickups might be easier to get a pair of coil splittable humbuckers that have the 4 wires that make this possible. Have a look on the PBG shop for Entwistle pups