Generally, I find it's easier to first fit the body to the chassis and then adjust the links to suit.
I measure the length of the chassis and find a body that's close. Then drop the body on and see how it lines up in relation to the bumpers...and then adjust the bumpers to suit. Once that's set up right, then I adjust the links to where they fit best....sometimes the front, sometimes the rear, sometimes both.
I have spacers I use to tweak wheelbase, or I use longer threaded posts from Axial. Either/or. I've made them from scratch in the bast, but with hand tools it's very much a pain.
Spacers:
Aluminum Spacers for #4 Screws
Posts:
http://www3.towerhobbies.com/cgi-bin...RCH=axial+post