You should replace the stock tubes and the suggestions above are good ones. The 5751 in V3 (front position) is very nice as it is more focused than a 12ax7 but IMO it is a little more analytical.
I would also replace the coupling caps. It is a far bigger improvement than tube rolling. Try Auricaps.
I would also replace the coupling caps. It is a far bigger improvement than tube rolling. Try Auricaps.