I did draw up a list which helped Els to generate the Equator and Arctic connections but here are the details that I came up with.
It is slightly different to what you ask but I hope it is of some use.
WHS that sit on major lines of Longitude/ Latitude
Prime Meridian: Greenwich*, Mont Perdu*, Tomb of Askia in Gao
Anti- Meridian: Wrangle Island*
Arctic Circle: Struve Geodetic Arc (I am sure there is a monument on the arctic circle but I could be wrong on this)
Tropic of Cancer: Buddhist Monuments of Sanchi
Equator: Lope - Cultural Landscape of Lope- Okanda, Mount Kenya, Galapagos Islands*, Quito*
Those with * are directly on the line the others are within 10km