I'm not certain of what you are asking, but let me give it a go anyway.

With either the Monte Carlo or the Master Time, you will need a specially-made back-plate to mount the timer to a flat surface. There is a bayonet system, etc.

If you have each of these two timers on its own back-plate, then the question is whether you can consolidate them onto a double back-plate (with the bayonet system) or whether the two individual back-plates for the MC and MT can be mounted on a single plastic plate.

Have a look here -- http://www.onthedash.com/watch/back-plate-plastic/

And also see the photos below.

Jeff

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: I'm curious if anyone has the rally-master backplate (ref. 61) from
: the early 80's. Would like to see a photo of it by itself. Is it
: just a piece of high-impact black plastic? I've acquired both a
: Master-Time and Monte separately and wondering about the
: backplate, and whether it's even needed...

:
: Source: onthedash