I've just bought one of these to help set camber front/rear as well as castor. At $150 landed I figure it will pay for itself in time.
Chevelle Billet Caster Camber Gauge w Magnetic Adapter | eBay
When setting toe, a tip from Warwick is to run some tube off the bumper mounts across the front and rear of the car. Once everything is squared up and centre line marked, it's easy enough to run parallel string lines along the side of the car and adjust the toe from that.