First can I say that although it is called Down Tor row it is actually on Hingston Hill SX587692 is the position of the cairn. You will find O.S. outdoor leisure map No 28 very helpfull.
Your best way is to first go to Dousland , turn towards Burrator at the Burrator Inn. When you get to the dam at Burrator do not turn right and cross it but go straight on untill you get to a small bridge, Norsworthy Bridge. Park here, there are a number of spots around. Grid Ref SX569693.
From here you can either take the most right of the tracks and head on through Middleworth to Deancombe and then go over Combeshead Tor to Hingston Hill or you can go up over Down Tor and across the Moor to Hingston Hill.
If you need any more information you can email me.
Peace , Lubin