I use Dacron fishing line, and put a straight pin in the front center of the fuse to align the stab. once you get the stab centered by measuring equal amounts from fuse to stab leading edge tip mark those points with a pencil/stickpin/sharpi.its pretty simple after that. if you have to mark a wing for mounting bolts do just the opposite measure from the rear fuse center to each trailing wingtip after the wing is centered. when you do this if the fuse is odd shaped or is a biplane you can reference the wings for the stab alignment. leveling the horz stab. I level my building surface and set the horz stab on cans, then shim the fuse up to the stab. the vertical stab is pretty easy after that just use a triangle like was said here.