Your horse is already out of the barn since the factory front axle is gone but what we do is make a plumb bob "T" pole with the leg tacked to the cowl/firewall and a plumb bob hung from each arm so the string hangs exactly through the center of the old spindles with the wheels straight. Put the new front end in with the strings in the center of the spindles and your dead on. A bonus is it leaves both hands free to juggle around what ever without using a tape. Do not change the angle of the frame till the new front is tacked in place as the change in angle throws the string off.

Evan