Rail pickup construction

[pulpadded]

I am mostly interested in making rail pickups. I was under the impression they used the same formula as PAFs and Duncan hotrails, with a single magnet down the middle.

Looking at the bobbins and magnets I got from Mojotone, that seems to not be the case. They seem to either use multiple magnets or magnets on the outside of the coil.

Is there a resource for construction information on full size rail humbuckers and single coil sized humbuckers?