“Airways equipped”/”IFR equipped” – what is the specific kit that should be present in a light aircraft for it to conform to this description?
You need to refer to Schedules 4 and 5 of the ANO.
"Airways" is standard 6 flight instruments with a second altimeter, COM/NAV/ADF/DME and Mode S transponder. In practice it should have BRNAV, but it is in principle "airways" without. "IFR" is much more vague -- could be anything.