There is no way to predict the way such a badly butchered frame will respond to street driving, energetic or otherwise. Boxing the frame usually results in the formation of stress cracks and other undesirable consequences, but people persist in trying to "improve" a design that was developed over a long period of time by some very skilled engineers and performed admirably for decades.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!