Nuts ...
and how do you cover this?
http://www.megalithomania.com/show/site/933/2807
This is nearly as tall as the chamber in Newgrange. It would need a 60m diameter mound to cover it in a stable manner. Pentre Ifan would need a cairn 35m across.
or
Trethevy or http://www.themodernantiquarian.com/post/21304 or http://www.themodernantiquarian.com/post/29934 ?