I'm pulling the 3800 from my '04 LeSabre due to a knock. I noticed that the bad motor has the Dorman 615-180 UIM. My understanding is that is better than the factory design.
The used engine going in, has a GM UIM, and looks like plastic gaskets on the LIM, so I plan to redo both. Can the Dorman intake be swapped over, or do I just need a new one?

I highly recommend doing both the lower gasket, upper gasket and a new plenum. Use the metal framed gaskets. They last longer.

Seconded. It'* cheap insurance, especially with the engine out and accessibility at its best.