The sly, cunning trick is to take a machinist's ruler to a commercial turnout, to get the dimensions of the flangeways. You also need to take the back-to-back dimension of your wheelsets, to assure an adequately wide check gauge.
There really is very little difference in the process of building large scale/large rail turnouts and the same thing in Z scale. The biggest difference is that in 1:80 (code 83 or 100 rail) I can accomplish with a few file strokes what you will probably want to do with a belt sander or abrasive wheel.
Good luck - found at the intersection of preparation and opportunity.
Chuck