If I do a poor mans alignment I Jack up the truck, Spin the wheels and make a line in the center of the tread on both ( as dan said ), then roll the truck forward a couple feet to " load " the tierod ends ect. I then measure the front and back. I set them up at 1/8 inch or there abouts toe in.
__________________
89 dodge 3/4 4x4, A727 ,3.07 gears, factory L S , powerstroke intercooler, S300, stans exaust with stainless tailpipe, fuel power screw turned?, fuel pin turned to deepest, 3 turns smoke screw, 1/2 turn down on starwheel.

93 W250 ex cab, 6X16's, 60 GDS, rag