Doesn't the actual tube itself slide in to the pumpkin. Cutting the tube off flush with the pumpkin then trim to give you the width you need. Cut the rest of the tube out of the pumpkin. Slide the rest back in. Have them fully weld the tubes back in. Yes you have to move spring perches and shock tabs. When you weld on tubes there is always a chance of distortion. I'd find a place to cut it off from the wheel end.
It does slide into the pumpkin but, factory tubes arent fully welded around to the pumpkin. So why would you do it to the shortened tube? You also dont cut it flush with the pumpkin.
You get the pins, that hold the tube, out.
Then you pull the tube out. cut the amount you want off (1" or less).
Then you slide the tube back in and make the end accept the factory mounting style.
The only thing that holds this up, is that the factory axle tubes diameter are smaller where it goes into the pumpkin compared to at the wheel. You only have an 1" or so, on each side, to cut off there. Compared to welding, this way has virtually no heat. he couldn't do it this way anyway, since he wants 1.75" on each side.
You run a bigger risk distorting the tubes, welding them back together after you cut a section out. As long as you get a good solid jig and you know what you're doing or are fully confident the guy your paying does,then he'll be okay
Doing it at the pumpkin gives you an advantage in one situation. If you are getting rid of the perches and shock mounts to do a custom link setup.