JeffL,
You ended your message above by saying "both measurements should be the same". I believe this is incorrect, there needs to be some Toe-In so as the truck rolls forward the truck will track straight.
My 1957 Shop Manual calls for 1/4" Toe-In, which means the front measurement will be shorter than the rear measurement.
Mike B

Mike you are correct, I should have mentioned there may or may not need a slight toe in, not all trucks require this. The straight on measurement will at least get you in the ball park.
I usually start there and make further adjustments as needed.
Thanks for pointing that out.