hi! welcome to the boards. to answer your question, it's almost impossible to replace the 4 with the V6. Notice I said "almost." You would basically have to change out everything forward of the firewall. The cost of doing that would be more than a good MX6 LS that already has the V6. i'm in the same boat as you basically. i've got the 2.0L, but that's a good engine to build from. Look in the Performance section of the 2nd Gen forum for a good article on how to beef up our 2.0L engines.