You only need 1 cam shaft for a VTR, vernie rpulley will get more out of it because it canbe dialled in accurately. But you could also say 3rd party management or remap would help along with a manifold, head work etc etc. The key is knowing what you want and where you intend to stop really mate.
Most will say to chuck a VTS engine in because it is more cost effective. Best thing to do is research on here what others have done and what they have managed to get out of it and go from there.