Many times when it comes to these issues it depends on how the vehicle will be used and what tires you will be using. If you can't hook that horsepower to the ground the suspension and driveline mounts won't see that much stress and strain.

But when it comes to boxing a frame I am of the opinion that if you have the tools, skills and ability there's really no reason not to.

I'd suggest setting the boxing plates into the frame and then attaching them using a groove and fillet weld, that's how I did the last frame I boxed. I also recommend notching the end of the boxing plates, looks like this:

http://i645.photobucket.com/albums/uu176/lakeroadster/1927%20Ford%20RPU/Untitled_zps1ef78597.jpg

http://i645.photobucket.com/albums/uu176/lakeroadster/1927%20Ford%20RPU/200305DSCF0030.jpg

In the Stovebolt Gallery ~~ "The Orange Crate" 1965 C10 SWB Step Side Build Thread

Inspired to be different. Different in a way of my own, not in a way that others strive.