My engine is a Lycoming O235 L2C.  It came out of a Cessna 152.  The engine sat for around 10 years before I purchased it.  The crank and rods had pitting corrosion beyond limits.  Yay.  The case was sent out and certified as well as the rest of the steel.  I elected to install new Millenium cylinders since the originals were an unknown.  I made a plenum with custom baffles.  The aft baffle was salvaged from the 152.  I added a 4 inch Saber prop extension.  Ignition is via Pmags, and for carburation I installed a Rotec TB40.  I found a Vetterman crossover exhaust.  It fits very tight around the sump.  In spirit with the RV crowd, I made my version of the "filtered air box" that ties into the carb heat muff.  Electrical power comes from a B&C 40 amp alternator with its matching regulator.  I found a lightweight starter to replace the original.  That saved around 5 lbs.

Roger's KR2S

The engine mount ring started life on a C152.  I tack welded the mount and had it welded.  After initial weight and balance, I needed to shift weight aft.  Fortunately, I was able to move the engine aft about 2 7/8 inch.  Of course I lost room for working on the engine.  Using Pmags, I was able to relocate the coil section of the mag.  Also a remote oil filter adapter was required.