I recently stumbled upon this website....http://www.milzymotorsports.com/

They're showing this; L67 Swap into 95-99 Monte Carlo/Lumina 3100 (http://www.milzymotorsports.com/miva/merchant.mvc?Screen=PROD&Store_Code=MMS&Product_Code=L67S9599LS).

What is an L67? Is this engine better than a 3400?

They say it Includes: -L67 Engine w/ 30 day warranty -4t65eHD tranny w/ 2.93 gears -all new hoses and lines needed for the swap -all other necessary parts and fluids -Walbro high performance fuel pump

Would I need to change anything else?

This the supercharged 3800, not just a direct swap from a 3400. Look into this further.