From the exit of the Taumarunui-Ngapuke Road turn right (West) for 1.3 km to Pukehou Road on the left. Take this no-exit road for 6.5 kms down to Kakahi where you have to ford the Whanganui river if it is low.

Kakahi is a small settlement with a small store.

After going through the village proceed south along Whakapapa Road for 7 km to Owhango.

From Owhango proceed 2 km East along Whakapapa Bush Road to a bridge over the Whanganui river to the start of the 42nd Traverse Track.

Report from a though-hiker: The next morning I hiked East out of Taumarunui to the intersection with SH41.  Several kilometers (four, I believe) East along SH41 I hit a small paved road, Pukehou Road.  Pukehou goes South from SH41.  NZTM coordinates for Pukehou Road are E1806505 N5692459.

I followed Pukehou Road 6.17 kilometers to it's end with a quarry road.  There are nifty kilometre markings along Pukehou (along with
one specifically for 6.17!).  When I hit the locked gate for the quarry road, I headed Left (East) to the Whanganui River. There was a
small farming road with a locked gate (hopped over), leading to a rocky shoal.  When I attempted to cross the Whanganui River it was
completely flooded!  I had to double-back.  Drought + heavy rain = badness.  The river was quite wide, deep, and fast moving.  My aim was to cross the river and follow along the banks of the True Left down to the village/town of Owhango to the South.

Well... flooded rivers that appear more'n chest deep and are 60+ feet across I just wasn't up to at that point.

From Owhango I hiked East to the 42 Traverse.  The 42 Traverse is a well-known bicycle/motorbike/four wheeler track.  Ask anybody in Owhango and they can tell you where to find the track.