Dreadman, my measurements are similar to yours - except for the saddle slot on my 18SW, which is .120. Do you have a suggestion for the saddle height? I assume I should aim slightly high, so people can adjust action as necessary. This one is measuring .3265 from the base to the top of the crown at its highest point, but it has been sanded.

SPT, my first casting here will be with Smooth-On's Task-9 as the base; I've got some Polytek 15-3 on the way. A guy at Smooth-On told me they have a couple other formulas that match our needs better, but the complexity and precision of mixture is quite high; he suggested I start with the Task-9, and move to those if it looks like I'm going in the right direction.