1996 with the roller rockers. I NEED an UIM, mine has a bolt hole broken off. I was replacing the head gaskets and during reassembly noticed it was gone, number 11 on the bolt pattern if you are curious.

I really dont want to swap heads, I just paid $250 to have mine pressure tested, valve job and milled, and I have installed felpro aluminum gaskets under the LIM.

Is keeping the heads on my 3100 and swapping the rest worth the effort? Im already buying an UIM at the junk yard, but I'm worried I will have wasted $60 on the LIM gaskets if I swap with a large port LIM.
Can I reuse this gasket with out having ran the engine?
Also if i find a 3400 engine from that gen, will my egr and coolant tube be compatable as is?

 

Some of the answers may be found in the service manual, (maybe) what might be the trick is to contact one of the engine rebuilder companies.
(Like jasper engines) and see if they can answer the questions.
You are gonna need to find someone here that had actually completed the task you are wondering about.
Yet there could be that one individual that will say ya!
We did have a fellow who swapped out the 3800 for a new 3800 with great success about a year ago, in his 98 Monte.