I have rebuilt the main steering shaft in my car. IF your shear pins are broken, then it's likely the car it came from was in a minor front end accident OR the column was bumped during shipping or something.
Anyway, what I did on my partially collapsed steering shaft (with broken shear pins) was to put one end in a vise, but vise grips on the other end & tap the vise grips with a hammer until the center shaft slid apart to the correct length.
Then, I drilled two 1/4" holes through the inner/outer pieces of the steering shaft & tapped it with a 1/4" tap. I picked this size because 1/4" nylon bolts were available in the plumbing department at my local hardware store. I screwed the nylon bolts through my tapped holes & then cut off the excess on both ends with a little dremel cutoff wheel.... viola, new sheer pins.
Personally, I would not tack weld the steering shaft (aluminum pop rivets might be OK). I have had some pretty nasty accidents over the years & I don't like the idea of being speared in the chest with a steering shaft....just sayin.
70 Roadrunner convt. street car
440+6, NOS, 4-spd, SS springs
'96 Mustang GT convt. street car
'04 4.6 SOHC, NOS, auto, lowered
"Officer, that button is for short on-ramps"