Have a look at the YouTube vids posted by 'Ricks Fishing and Leisure. He appears to be the owner or a senior staffer at the ITM in Taupo. He nymphs the Tongariro in winter, then does a fair bit of jigging in the warmer months - launches at the ramp in town and fishes mainly off the likes of 5 Mile Bay by the look of it. The landscape in the background is fairly recognisable.

He doesn't go into much detail about his rigs etc, but you can't go wrong with whatever pre-made Pat Swift ones that the local shops recommend - remembering that the smelt tend to be a different size and colour than in the Rotorua lakes.

I always used to tie up some Parsons Glory flies with a fluoro green body, which was an old favourite of some of the Taupo harling stalwarts. 

I would think the contours across the whole bay off the mouth of the Waitahanui would be a good spot to try, it's always been a highly recommended area for harling (keeping in mind the legal distance you have to keep from the river moouth). My feeling was that the fish running up the Waitahanui are a bigger average size than some of the other rivers, and there are some decent browns living in that bay too.

Looks like a general line between Wharewaka Pt and the end of the cliffs south of Waitahanui.  Maybe shallower first thing, deeper later.

You might get a few spent fish this time of year as they start feeding after spawning, mixed in with a few maiden fish.

I'm heading down to Turangi for the first part of the second week of the school hols, hopefully still a few fresh fish coming through. Usually in spring the little naturals can work quite well, and I have a special little caddis that will be my go to.