Unfortunately you probably won't find much remaining of the barrow that was here. But it was surely carefully placed here at the source of the river Gamber - the Licat Amr - the eye of the Amr.
Nennius wrote about the grave:
There is another wonder in the country called Ergyng. There is a tomb there by a spring, called Llygad Amr; the name of the man who was buried in the tomb was Amr. He was the son of the warrior Arthur, and he killed him there and buried him. Men come to measure the tomb, and it is sometimes six feet long, sometimes nine, sometimes twelve, sometimes fifteen. At whatever measure you measure it on one occasion, you never find it again of the same measure, and I have tried it myself.