The procedure I adopt for pretty well all the girders I build is the much the same. In a nutshell:-
1) Put the steering stem and top clip in place (roughly adjust the head races at this point)
2) Put the spring on the forks and fit the lower spindles. (the fork blade is now swinging/hinged in the middle, so some protection for your paintwork with rags or cardboard is advisable)
3) Enter the top of the spring into the top clip. (a bit of force or bending the spring is needed, but I always manage it quite easily on my own)
4) Now strain the top of the forks into place to line up the top links.
5) finally adjust the links and head races as required.