Yes, either a wedge (thick end faces forward) or only shim the front bolts, etc.
The trail is harder to figure, since it involves the front wheel & tire radius as well as the design of the KP (not just its inclination). Even very low caster ("rake" in a motorcycle) is stable if the trail is enough. This is the distance a theoretical line drawn through the KP axis intersects the ground, compared to a vertical line through the spindle, in inches. Zero trail is a shopping cart.
