Often the dovetail is missing, but it has
a pair of dowel pins for alignment and a
screw, so if you have three holes on the
left end of the saddle then that is where
the dovetail once fit.
there are also bed stops available that
work with the indicator, and there are
other devices (e.g. a non-adjustable hard
stop) that fit on the dovetail. The indicator fixture also comes in a variety
that fits the right end of the saddle.
My 1940 EE takes a different indicator and
holder, even a slightly different dovetail.