Yep, I know the problem. I spent many, many hours, over a number of weeks, trawling through photos, diagrams and drawings, and some modelling articles, including looking at after market accessory parts that didn't identify what the equipment actually was,, although it matched what I was looking for, trying to find a definitive answer. I ended up being totally flumoxed by the various TR and SCR numbers and derivatives.
This was even more complicated when Canadian built Mossies were illustrated, which were, or could be, equipped with American - sourced radios, instruments and some other items, and many close-up photos,showing the cockpit externally, looking in, lacked detail of the Mk in the captions.
The fit of the 1155 certainly seems to have been used, in the early days of 'Gee', and, of course, continued with some of the B.IV and PRU aircraft, including later PRU variants such as the Mk.IX, and it was certainly fitted to at least early FB.VI models - the mast is the indicator of this - and here lies part of the confusion, if that's the correct term in this instance.
Eventually, I relied on info I'd gleaned from those Mosquito crews I knew (now all sadly passed on), who's descriptions tallied with the layout of the two, rectangular boxes on the spar 'shelf', with 'Gee' alongside, seen, even vaguely, in some photos, and which corresponds with the internal, or whip aerial which would indicate VHF radio.
My conclusions were that, if it's a 'standard' FB.VI,
without the aerial mast, then the two rectangular boxes, one of which (port side) is the Gee R/F unit, should be the layout.
If it's an earlier FB.VI,
with the radio mast, then it could have the 1143/1155, or the 1143 and Gee, or a combination of whatever - only detailed photos / info could perhaps solve this.
Of course, the role / unit and operational area can also have some influence. as radio frequency range may dictate whether HF or VHF radio is required, and then more complications could arise, depending on variant of the radio, for example 1155, 1155A etc, , and whether there are one or two antenna wires !
Bottom line for me, unless there is photo evidence to prove otherwise - if there is
no aerial mast, and it's a FB.VI in the 'standard' role (eg with 2 Group / 2 TAF, rather than 'specialised roles, such as Banff Wing) then it's virtually certain that VHF radio is fitted, and most probably, the 'two boxes' type.
Note though, that it could be VHF, with Gee, and employ the American SCR 522A/542A sets, ( pic from manual below) which retained the mast, but without the wires or wire attachment, similar to, for example later Spitfires, the size of the 'boxes' being more compact then the 1155, but slightly larger than, and mounted in similar fashion to the equipment mentioned above. But, from what I've learned to date, this was fitted to Canadian built aircraft, and possibly / probably Mossies in service with the USAAF only
I'm still looking though my references, a bit at a time, to see if I can fin the pics i based my conclusions on.
EDIT: Forgot to add - yes, the Gee IFF controller is shown starboard side, where the fuel gauges are, although I haven't seen any details on it, and assume it's a small unit, within the panel where the gauges are. as it would only be a couple of switches / relays - and, on checking, that switch box is related to the Gee.