In 2003, at overhaul I converted my O-470-K engine to the carbed IO-470F per the Norland STC. As I recall, the difference was the (exchange) upgrade to the heavy duty 520 crankshaft, HD connecting rods. The upgrade required the heavier cylinders with the deep reach plugs, and domed Pistons (hemi-like)and as I was purchasing new cylinders at the time, the cost was the same.
So, cost at overhaul was maybe 10% more than if I had stayed standard.
The extra 30 hp is nice, performance is great, fuel consumption essentially unchanged.
However I do have mixed feelings on some of the trade offs going to this high compression engine.
1/. I operate mostly on floats, and over the 38 years of ownership, I have on occasion found myself needing to hand prop with a dead battery or failed starter. Back in the day with the O-470-K I could do it. Now with the hemi - not a chance. Too much compression. Of course, now I have the upgraded firewall battery and HD starter so hopefully hand propping should not be required.
2/ although I always traditionally fueled with Avgas, after 80/87 octane became obsolete, I could on occasion supplement the 100LL with auto fuel premium unleaded or even marine fuel in the K engine while in the isolated far north. Not any more ... It has to be 100LL for the high compression engine.
3/. I had to upgrade the prop to accomodate higher HP. That was an expense and
the STC called for the 2 blade McCauley D2A37C230 which came with that lousy new shinny pointy spinner. The backing plate is inadequately designed and prone to cracking. It has been a bit of a curse and the 3 blade is not approved with my STC.
4/. I now fly about 50 hours a year, apparently not enough to keep the IO-470 cast domed pistons from pitting corrosion. With only 700 hours, I recently replaced the pistons due to corrosion. Apparently the standard O-470-K are manufactured by a different process and not vulnerable to this pitting. Also, my cylinders were new ECI, so I am having to work through the recent AD thread.
FWIW, these are some of my reflections on my 260 HP Norland STC upgrade experience.