If you want a V6 it would be more cost effective to buy the whole car.
For tuning as said before autodelta do it but are expensive. They can turbo/supercharge your 2L(if you have deep pockets)
See Link
http://www.autodeltashop.com/index.php?cPath=30_84
If you had a V6 in the first place the capacity can be upped to 3800cc then supercharged. 405BHP will see off most things if you can get the power down