Cheaper to just get your heads skimmed etc than buying new heads (unless you can get them dirt cheap, and if u can then there is probably something wrong with them)
Remember the VT's are a roller motor, so as far as I know you would need a roller cam and roller lifter not the standard flat tappet lifters and cam setup.
It doesn't cost much to get headwork done to yours so just go that way (a good set of VT heads will probably be $4-500)
Go to Leon at awesome automotive, he is the only tuner in Adelaide I would trust with my car (he is widely renowned as one of the best V6/5L tuners in the country, people bring cars from all over to see him), you can't call him though, he is so busy he won't answer....you need to drop by and see him