I've always gone by So-Cal Speed Shops recommedations on setting up a solid axle front end.
Between 5 & 9 degrees positive caster (king pin leaning back) and 1/8 inch toe in for radial tires and 3/16th inch for bias ply tires.
I personally usually go 7 degrees positive caster and that seems to work well.

I'm not sure how much adjustment you have using the stock wishbone. You may have to V cut the wishbone to get your caster correct.

Mick