What would be the easiest or best way to swap my 99 monte Carlos 3100 to a 3400 or 3800 as in the best donor car or most compatible engine with my 99 monte

 

any 3400 w-body, 2000-05 impala/monte

 

A 3800 swap requires a few extra things. Can't remember them all but I know that you'll need a wiring harness from a 98-99 Monte Z34 or Lumina LTZ. But like l67ss said, if you want a 3400, I'm pretty sure it's as easy as pulling the 3100 out and putting the 3400 in (as long as the 3400 is from a w-body).

 

I agree, a 3100-to-3400 swap should be easiest (and there is a member who posts from time to time who is actively doing a swap now). Here are a couple of links in our tech info section to info about this type of swap:
https://montecarloforum.com/forum/fw...ne-swap-46706/
https://montecarloforum.com/forum/fw...00-swap-40684/