I'm looking at buying a Cessna 175 with a bad engine. I spent days searching and reading. But most of the info is repetitive and dated. Most if not all of the STC info I can find is 10 or 20 years old. The STCs are hard to get, sometimes impossible, and the only one that isn't is Stoots, and that is more money than I want to put in this plane from what I hear. I called, but no one returned my call. I'm not against putting the plane into experimental, But I'm trying to exhaust all avenues before giving up on upgrading the engine. People say that you can't get parts for the G0-300 and others say that they are still rebuildable.
Any advice other than "I'll take it off your hands"

The cost to modify one of these airplanes with an upgraded engine is crazy right now. Dave Stoots will answer your questions, give him a call, leave a message, he'll get back to you. Ask him what that price of the STC includes. Generally, the cost of a current STC typically is not just the paperwork. It includes proprietary parts as well, like an engine mount. And, STC or not (ie: if you go to Experimental/Exhibition category), you still have to come up with those parts from somewhere, and often, the only source is the holder of the STC. Parts such as engine mount, exhaust, cowling mods (if needed), plus an engine, propeller, etc, etc.

So, IF you were to go with a Lycoming O-360, for example, I doubt if you can find one of those engines in decent shape for less than say, $50K. Add $15K plus for a prop, plus other accessories (look up some pricing on things like starters and alternators, oil coolers, etc, etc) and you're going to have well north of $70 BEFORE you hire someone to do the work (around here, good mechanics are charging $120/hour), and that's going to be well north of 100 hours, I'd bet.

And, my understanding is that the STC to install the Continental IO-360 engine in the 175 is still available. I'm guessing those engines MAY be a little cheaper and easier to come by than Lycomings. Maybe.

Again, understand that even if you call it Experimental, you'll have most of the cost in the plane anyway, but the value of the plane likely will suffer at resale. Oh, and by the way, the FAA is pretty lenient in the Experimental Exhibition and Airshow category at the moment, but that category has been "discovered" by quite a few folks, and it wouldn't surprise me a bit for the FAA to crank down on the provisions of that category. If that happens, you are essentially screwed.

My understanding is that the GO-300 CAN be overhauled today. Do some research, make some calls. That is the way to go, frankly. Either that or purchase one that's already converted. I see a few occasionally needing some love selling for "reasonable" prices.

Whatever you do, stay far, far away from a guy named Williams, who currently owns the AVCON engine conversion. IF you can get in touch with him, he MAY sell you paper, but I wouldn't bet that you'll ever see that paper. Beware.

This is from the owner of a 1958 Cessna 175, with AVCON engine conversion and Bolen tailwheel conversion. Mine was already converted when I bought it. I've also put a lot of $$ into it in upkeep and repairs.

Stoots is by far the most complete and best bang for what you get.

The engines perform well exceptionally well.

If it is a long term plane for you thats the way to go if its only a stepping stone or project it may not be worth the extra cost.

Be aware of the high cost of overhaul for the GO 300 as well seen some horror stories even with straight 300s.

An additional comment: If you were to start this "project" with a REALLY nice condition plane that just needs an engine, as in decent avionics/paint/interior, mechanicals, and you don't pay much for it to start, you might come out not totally losing your shirt if/when you sell it.

On the other hand, if you put $100 K into a rat bag of an airplane.......you'll still have a rat bag, but with a nice engine.

Run, don’t walk away from a project like that unless you are doing it as an exercise.
It makes zero financial sense and will probably take 3 times as long as you think it will. Finished 175 conversions are out there.