Do you have another LH gasket, maybe that will work for the short term. Some of the 68/69 passenger side mirror gaskets were made with the wrong angle that they still work and only notice the difference if you look very close. I don't know what the 70 gaskets look like so it may not be possible.
Just a quick heads up, and it could be that mine is incorrect, however; I replaced my RH remote mirror today on my '70 stage one and the gasket was marked (as you mentioned) l.h.a. Identical to the picture posted.
That's interesting. The one pictured came with a LH manual I got from a board member a couple months ago. Perhaps that's not the correct one but I feel like they'd function the same.
