I don’t believe the version of Monica in A.R.I. 5122 had an indicator – it produced audio ‘pings’ which were fed into the intercom system. Later versions used an Indicator Type 6 (which looks superficially similar to the Fishpond Indicator and is the same overall size). I’m not familiar with where equipment was located in the Stirling, but in the Lancaster this was located on the Wireless Operator’s table. This can only have been in the position subsequently occupied by the Fishpond Indicator once H2S MkIIB was fitted.
Andy