For a cheaper solution I got myself a set of 8" callipers. Then just measure the front of the inside of the wheel then the rear, keep adjusting until the caliper reads the same in the front as it does in the rear of the wheel.
Even cheaper solution is to get a couple of long pieces of brass tubing the same size as your front axle 1/8 for the small and 3/16 for the large axles. Then slip one over each front axle and hang the chassis over the edge of the pit bench. You will be able to see any toe in or out with the extra length.