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.
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.