Have to manufacture a new crossmember for the gearbox when going from 4cyl to 6 cyl. A lot of messing around, but well worth the effort for the final result.
Not worth wasting time with the 4 cyl.
You are so lucky you had the option of a 4.1 straight 6. in the UK the biggest engine we got was the 2.3 V6 which was noteable for its great thirst in relation to the amount of power it produced.
There are plenty of mods you can do to the 2.0 4 cylinder though, if you are that way inclined, such as 16 valve head, twin 40's, etc.