I think the OP is talking in terms more like
this example.
Interesting as a project, but lots of obstacles to be overcome - noise, fuel consumption, Vne ...
Google the MC-15J and Sub-Sonex to see other peoples ideas in a similar vein.
Basic IFR isn't too difficult. All weather, FIKI, high altitude etc is another thing.
The GTN650 with remote transponder meets IFR nav/com requirements.