How critical is it, for purposes of safeguarding the viscous coupling, to
have a spare tire that is the exact type, size, and tread wear to that of
the other tires?

I have a set of four Bridgestone RD 603 tires, size LT 185R14.  My spare
tire is a Michelin XZX 185R14.  They are mounted on my 86 Syncro GL.

So far (crossed fingers here) I have had perfect performance with my
Bridgestones.
If I should happen to have to use the spare, how far/fast can I drive
without causing problems with my viscous coupling?

Would it make any difference if it were the front/rear tire that needed the
spare?
In either case, would it be helpful to remove the center driveshaft,
especially if it occured on a trip many miles away from a replacement
Bridgestone tire?

As always, thanks in advance for all responses.

Budd Premack
86 Syncro, 73 Super
Minneapolis, MN (Land of Sky-Blue Waters)