Radiator would be same (just decontent the engine oil cooler supply and return lines).
Different motor mounts.
It is said that you can make the existing a.c. lines work by slight bending. (some lines (new) can be hard to come by)
Other things that need to be dealt with, but not show-stoppers:
? Fuel evaporative system changed between some years - using the 300Ms PCM should take care of the fuel tank and sensor details if different, might need one minor tweak on the vacuum fitting (tee vs. elbow to handle extra line to fuel tank for some years) that goes to cruise control off of plenum - if 2000 and 2001 are same evap. system, then you're golden - need to discuss.
? The 2.7 doesn't have the SRV and MTV (for my swap years '99 2.7-to-'98 vehicle, the 3.2 PCM adapted to the non-SRV/non-MTV situation - not sure if true for all year PCMs);
Are you keeping the same transmission? If so, gear ratio is higher on the 300M transmission (engine turns slower for a given road speed). Could swap transmission or jut the chain/sprocket set in the transaxials if you have both. My 2.7 handles the higher geared 3.2/3.5 transmission just fine. That would allow you to stay with the 300M tranny and PCM to keep the speedo/odo readings accurate. You could always pick up used PCM and tranny or chain/gear set to match what you want for gearing if issues (for example, if you want to go with 2.7 PCM for gearing change, but fuel evap. system is different for years - you don't want to deal with making a PCM work for the other type evap. system - that's what forced me to stay with the 3.2 PCM that I already had).
Dan (Daytrepper) is *THE* expert on this (literally wrote a book on the opposite conversion, but definitely usable for the 3.5/3.2-to-2.7 swap - which I did).
'98 LXi - Later Concorde gages (black w/ chrome rings)/'99 LX - LHS gages (white) - HIR bulbs