Not much to say Derek apart from it looks like the passage is aligned on the solstice judging by GE and not the Mitchell plan but it is short (4m approx ) and uncovered .The Mitchell plan which is used in the Eogan book has a a northing that would typically be out by 10-12 degrees which makes it in agreement with what it appears on Ge and thus very close .
Interestingly George Eogan has a big plan of Knowth that is way wrong on one page then a few pages later it is corrected with the earlier northing marked as magnetic alongside the true northing which is bang on ( good ole G.E. a rare occurrence in them days and even much later )but the Mitchell plan in the same book doesn't have this .

We have a lot of the Archaeological Inventories and they bear no comparison to the megalithic survey books.

The inventories cover all archaeological sites, including Christian, monuments usually get a paragraph with no plan or photo. The survey books have detailed description, plan and photo for every site.

We drooled when we saw our first volume........

Maggie & Keith