I will soon be installing a Garmin G5 EFIS in my 53 C180. I got confirmation from the local FSDO that there's nothing in the regs to prohibit this installation: it's not a major alteration per FAR 1.1, it's not replacing any required instruments, the C180 was certified under CAR 3 which does not contain any TSO/PMA/etc requirement for instruments. Mine will be for VFR-only use, maybe if intended for IFR use it wouldn't be legal, or at least wouldn't be so easy to get them to admit that it's legal. I'd suggest maybe installing something like this, but retaining your old (required equipment) airspeed altimeter & VSI.

Re engine instruments, I'm pretty old school so am sticking with the stock analog stuff, but if I was to go digital I think I'd get an ECI GCR30. It would replace all my engine instruments (and then some!) & it fits in a 3-1/8" hole. Plus it's STC'd and all that, so should be no problem with approval. Personally I'd prefer flight instruments in one place and engine instruments in another, instead of everything jammed into one display, so would go this way instead of an all-in-one display.

Let me throw in come comments, not because I'm flying a 180, but because I'm flying an old airplane (63) with an old panel, and I don't like to spend more money than necessary, just like you guys. I've been IR for over 40 years, though at the moment since my airplane has been down for awhile, I'm not current--hope to solve that in the next couple of weeks.

When I bought my airplane, it had illegal 360 channel navcoms and OEM flight instruments and engine instruments. Over the course of time, I've replaced the navcoms with a 430W, the failed DG with a new DG, and just recently, the AI with a Quattro (reduces my concern about losing the vacuum system in the clouds). I added an ADF 10 years ago, which today I probably wouldn't do, but at the time, the FAA hadn't pulled very many NDBs. Since it works fine, I'll keep it. When I added the Quattro, I also replaced the transponder that I had installed 10 years ago with a new BK KT74 tied to the 430W, for ADS-B Out.

For the engine, I've added an Insight G1--I very much like seeing each CHT and each EGT separately, and it's easy to read. I have added an EI fuel flow meter/totalizer. The oil pressure and temp gauges are OEM mechanicals and work just fine. The gas gauges work fine, but if they didn't, it's not all that expensive to replace them with used ones--it's typically the senders which go, and they're easily replaced.

I also swapped out the 121.5 ELT for a 406 ELT ages ago.

I purposely don't add up everything I've spent, because it would probably convince me to quit flying. But I think by replacing things as they needed replacing, and updating on an as needed basis rather than going whole hog all at once, I've spent less, and it hasn't been all in one fell swoop.

Take my comments FWIW.

Cary