If welding on a steering shaft isn't illegal, it should be. It's slightly safer to do a sleeve and rivet coupling, or something similar, but I've seen some real disasters on the dirt track from welded steering worm shafts. If a part from a later-model steering column with the double-D-shaped tube could be fabricated, that would be the best possible fix. Trusting a simple butt weld with steering duties is a little bit foolhardy.
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!