Bob --

I just examined the rear glass of my '86. The center brake light assembly is glued to the glass.

I'd guesstimate that you could remove it using a new, clean safety razor and carefully cutting the adhesive where it meets the glass. At first pass, I'd say that the adhesive element is a rectangular black foam, double-sided sticky, that sticks to both the plastic housing and to the glass.

If you're careful, you might be able to reuse the foam by substituting double-sided Scotch tape.

You might be able to buy a replacement foam from Volvo for only $2,499.95 plus tax and shipping.

This is certainly a question a glass shop could answer -- they probably do this day in, day out.

"...fixed and pointing North northeast..."

But only if you're pointing north by northwest.
--
Don Foster (near Cape Cod, MA)