HD16 , he later used an HD11 . Article with the picture on google gives the impression he started gravity rolling without saying it , he didn't and by a long way .
Huntly Engineering Works (HEWCO) converted quite few C6 Euclid dozers for this work for various contractors back in the day. A later version of these has been morphed to a remote controlled machine assisting harvesters in the logging industry that work on steep country. There are some photos of them on the forestry operations section here. Its amazing how necessity is the mother of invention.
After the scrub was crushed the need to get fertiliser and grass seed on the ground was the next problem. It was overcome with another NZ invention, aerial topdressing
and the manufacture of the worlds first purpose built agricultural aircraft, the Fletcher FU24 a 225 hp. It also has been changed alot but looks similar to the original design. Some of you in North America may have seen it flying as the worlds only purpose built skydive aircraft, the PAC 750 XTOL. There are heaps of u tube videos to be seen for those interested.
