JohnO wrote:
What's the difference between an IGSO-540 and an IO-540? Can one be
conveniently used in an RV-10?

According to Lycoming:

http://www.lycoming.com/support/tips...%20General.pdf

"Supercharged Engines as manufactured by Lycoming uses a compressor
wheel to pack air into the cylinders; but the compressor is driven by
the crankshaft through an intricate gearing system, which takes
considerable horsepower from the engine to operate. In comparison with a
turbocharged engine, it is a medium altitude power plant.

Although supercharged engines could be built by Lycoming, new aircraft
designs during the past 20 or more years have used turbocharging instead
of supercharging because of the advantages that turbocharging offers.

A supercharged, geared, opposed, fuel-injected Lycoming engine with
cylinders of 540-cubic inch displacement is designated
an IGSO-540 model."