Go to a hardware store they should have cheap anglefinders that area around $5. Before you start put the finder on your front pinion flange, write that angle down somwhere. Now once you have the front suspension put in the truck, measure the angle again. From there its just simple subtraction and theres your shim need. Usually it takes a 4-6 degree shim to get in the ballpark. I like to run a bit more castor, so I dont use all the shim that I really should. But its a trade off for street manners vs. trail performance.
