Toe-in is 1/8" only, not 1/4".
You can tell if caster is right by how it drives. All caster does it use the weight of the truck to hold the front tires straight. With little or none, you get a very loose sensation in the steering wheel, it just doesn't seem to want to go straight at higher speeds or return to center after making a corner. If you get to much, (4 or more degree) you end up lifting the whole front of the truck when trying to turn at slow speeds and after making a corner the wheel wants to center up to quickly.
If in doubt, add a 2 degree wedge and drive it awhile. I believe 2 is really common for straight axles setting at stock height. Wedge goes with thick part towards the rear of the truck.
It use to be easy to find 1 3/4" wide caster shims, but now you have to go specialty shops.
Here is a place that sells 4 degree wedges,
http://www.truckcomponentsonline.com/TRUCK-CASTER-SHIMS_c_316.html Joe
