For an N-reg, the GPS approach requirement is met with an FAA approved POH supplement too.
It took me nearly a year, but I got it. The installers gave me the run around for a while, but finally got it all signed off by the Avionics Inspector at the London International Field Office. Anybody who wants to do the same should save time and just
buy my aeroplane, which is now so cheap as to be on sale for less than the purchase new cost of the avionics and instruments. Seriously. Buy a couple of Garmin GPS, an autopilot, an HSI, stormscope, etc. and get a free Cessna 182.