Yes this one's quite a tough race. Nav-wise it's not that bad.

From the start it's simple to the first stile, then follow the path keeping the fence to your right, over 3 more stiles untill you get to the stile by the board walks (the planks over the wet stuff) after them keep the fence to your left all the way to the summit, but after the planks you need to go right a bit to pick up the quadbike track to the foot of Aran Benllyn (pile of stones) then a scramble up for a bit to a small lake then follow the fence to the foot of Aran Fawddwy then scramble to find the trig point. Same way down.

Note!!!! when you descend Aran Benllyn (what you had to scramble up before) make sure you pick up that Quadbike track, Essential!!! to maintain speed and running, if you stay with the fence your in allsorts of rocks and boulders, totaly un-runable stuff!

I was up there on Saturday the course is running nice at the moment, I'll be there but marshalling as I've a Duathlon the day after.
Enjoy :-)