Iits harder to get all the weld out that hold the tubes to the center section. And you still need to shim the center for pinion angle. Most will grind out the welds that hold the knuckles to the tubes. Then the knuckles can be beat into position with a hammer and rewelded.
I hope you're not thinking of actually cutting the tubes. Major problems with strength and alignment will result.

Yep that's a 75-90 kingpin axle with external lockouts. The 91-93 trucks had different lockouts.