Jackyl there are a fair number of people who say they have swapped the 1/2-ton front axle onto 3/4-ton trucks. The 1-ton is very similar and I'm imagining it would not be hard to swap the axles but you need to be prepared for some adapting as you proceed.
The bigger the truck the more likely Chevy vs. GMC will make a difference, but in a case like this it should not matter. Be aware that one popular upgrade is to use the 1-ton tie rod because its easier to use later tie-rod ends.
The frame on a 3800 is made of heavier material than the 3100 and the frame rails are both taller and wider. Also somewhere under the cab the width of the frame begins to differ and is narrower all the way back from that point. And of course I'm completely ignoring the 21 inch difference in wheelbase.
I'm sure I am one of those who has said the axle swap is possible. But before you begin you might want to spell out your entire plan to be sure I and others are not answering questions making assumptions about what you are doing that don't fit your objective. While I recognize your name and know I've been part of previous threads about your truck, you'll want to refresh my memory about what you are doing. I can hardly remember the details of my own projects, let alone those I comment on...
You might also want to indicate your own skill set and access to tools or perhaps those of the friends or shop you plan to use. Some things are easy if you have a full shop and good fabrication skills, but may become very difficult working in a driveway with a Walmart 62 piece tool kit.
You say your location is New York. Working in a parking garage stall in the city would be a different ball game than a car port under eight feet of snow in Buffalo. And either is a lot different than using your brother's three-bay shop with a lift, three welders and a machine shop in the basement. If that does describe your brother can I borrow him?
