I boxed the front of the frame back to about the leading edge of the door with 1/4" plate. Additionally, there is some reinforcing going on around the steering gear box. The truck got 4 more crossmembers and the rear is bolted to that water/alcohol tank which is made from 1/4" wall aluminum and is bolted to each frame rail right at the back end. That entire area has quadrupled in strength over stock.
Now having said all that, and most people will disagree with me (and they would be wrong) with respect to this series and similar trucks, the frames need to flex. I know...runs contrary to modern convention, but frames of this vintage that are all boxed up have shown severe cracking at specific locations, whereas, I have at least one guy on my website who is rebuilding his crew cab mid 80's Dodge for the third time. Second iteration accumulated in excess of 300K. He photo'd the frame following extensive cleaning and media blasting and that sucker was stock and showed no cracks!