I did a gen III (2004 5.3L) swap with a 4L60E in my 71. It all depends on what you want to do with it, you could drop it in with your existing transmission and run it carbureted, get an aftermarket controller from Holley, Aces, Summit, etc., or do like me and integrate the stock LS computer into the Monte's wiring harness.
My engine was out of the junkyard with 124K miles and the transmission was a rebuild with some of the stronger components. The mounts are polyurethane small block mounts with adapter plates that put the front of the LS in the same place as the stock engine. That let me use the stock TH350 linkage because it was in the same place as the shifted 4L60E. You can use a GM F-body LS1 oil pan instead of a more expensive swap pan because the Monte Carlo crossmember is further forward on the engine than it is on a Chevelle.