I'm in a similar situation: IFR certified C-150M with a single Narco
MK-12D that has Mkrs, GS and DME and a ARC ADF and a Narco LORAN. I
thought about replacing the Loran with a GPS and decided a handheld
was good enough for VFR/SA--an IFR GPS is too expensive to install and
too expensive to maintain with a current database (on a C-150 budget).
I bought a second Narco Mk-12D (vor/loc only) and plan on removing
the Loran. I'm conflicted about retaining the ADF as it still works
but is such a boat anchor I'll probably either remove it or move it
and its indicator to the glove box area. If relocating it costs
significantly, it will be tossed. This will give me room to move the
transponder to the center stack (from the glove box area), have two
nav/coms and a new audio panel all close at hand in the center. Two
comm radios makes it nice to monitor ATIS without having to go off
freq with ATC. Two navs simplifies the 30 day VOR check as well as
making intersection ID much easier. IFR GPS is certainly nice but I
couldn't justify it in a C-150. I already have DME (IDME 891) so
there is less of a requirement for the IFR GPS. The Cessna 150/152
panel is certainly space challenged, but maybe that's a good thing