10. With the crossmember and coil spring towers removed, we're now past the point of no return. No worries, right?
11. The stock Ford truck frame, while plenty strong, isn't exactly stiff. This is one of those frames that can really benefit from a boxing job and that's exactly what we're going to do. I picked up two 36x12-inch sheets of 1⁄4-inch steel to do the job. I clamped each to the corresponding framerail before tracing the shape onto the plate.
12. While 1⁄4-inch is a bit overkill for boxing plates, I had the ability to cut it and that's what the metal yard had in the remnant pile, though 1⁄8- or 3⁄16-inch plate would be fine. Here's the traced pattern, ready to be cut with the plasma.
13. With the framerail marked, the new crossmember can be lifted into place and centered in the chassis. The axle centerline corresponds with the center of the crossmember. I like to measure five times and cut once, so here I'm taking diagonal measurements to ensure that the crossmember is nice and square before I tack it to the framerails.
14. With the boxing plates tack welded to the framerails this is where the laser level really helps out. When set across the two axle centerline marks, it projects a vertical line that makes marking the axle centerline on the framerail a piece of cake.
15. Since the chassis is setup at the approximate final rake, the crossmember can be plus or minus one degree of level. I opted to shim the back of the crossmember just a touch to get it closer to level as the bottom of the frame curves slightly downward towards the front of the truck.
16. With everything triple checked, I tacked it into place. Note that the boxing plates haven't been fully welded at this point. I decided to wait until the crossmember was in place before putting too much heat to the chassis, just in case it decided to twist or get out of shape.
17. Next, it's time to install the shock towers. These need to be installed exactly 40 inches apart, as measured at the shock mounting holes. A piece of steel is used to retain the distance, tacked to each tower. It's important to also ensure that they are nice and even in relation to each other as well since they'll be installed on the chassis exactly as they sit.
18. Since frame widths can vary, the rear corner of each shock tower needs to be trimmed so that they can fit over the framerail perfectly. Before I placed the shock towers onto the chassis, I marked the center of each, which corresponds with the shock mounting hole. When the shock towers are trimmed and placed on top of the framerail, the alignment of the centerline mark on the bottom of the shock tower and the centerline mark on the framerail will ensure that the built-in anti-dive angle of the shock tower is retained, placing the shock hole centerline slightly rearward.