Regarding the use of mercury switches, I can offer the following two
suggestions:

(1) Replace the mercury with small, loose ball bearings.  Bearings of
the appropriate size will "flow" somewhat like a liquid and provide a
replacement for which there can be no worry regarding heavy-metal poisoning.

(2) If you use mercury, cover it with a layer of glycerin to prevent or
minimize arcing.

These suggestions come to me from rebuilders.  Since I have no direct
experience with mercury switches, I cannot comment on their usefulness.
I offer them for consideration and possible investigation by others.

With best regards,  Wayne Stahnke