Doh! I shot the alignment how-to video and forgot to post the link here.
You would save considerable time and increase your accuracy by finding a good-sized piece of sheetmetal, and cutting it into four pieces of perhaps 1' by 1'; smaller can work. You'd want the sheetmetal to be as thick as you can conveniently find--but it's not critical.
Put two pieces together with a bit of grease in-between. Place the greased pairs under each front wheel. Now you've got "slip-plates", you can make an adjustment, then bounce the vehicle on it's suspension, instead of driving back and forth to take the bind out of the suspension.
I would also emphasize that when doing ANYTHING related to alignment, the process should include finding the center point/high point of the steering gear, and then locking the steering by any means, including having a wife/neighbor/young child hold the wheel while you make the needed adjustments. (Finding caster generally involves swinging the wheels to each side, so of course the steering wheel has to turn for that.)