Additional resources and choices
From Matronics archive
http://www.matronics.com/rv-list/hovan/Vans/engine.html:
"...Not every O-320 or 0-360 will fit... Carburetors, fuel injectors, induction tubes, governors and other items have all been mounted in different places to satisfy the needs of aircraft designers..."
[support for Mel's response:]
"...Engine configurations that cause problems on RVs include HORIZONTAL DRAFT CARBURETORS or INJECTOR BODIES, that are mounted on the rear of the oil sump... Another problem area is the "H" engine. Lycoming produced an entirely different O-320 for the 76-77 Cessna 172. The fuel pump was mounted over the front left cylinder, the accessory case at the rear is integral and a different shape. As supplied, the RV mount will not fit with this engine, but modifying the mount is not difficult, and several RVs have been flown with this engine. In general if the induction system faces forward or is mounted toward the front of the oil sump then interference with the mount itself is not very likely...
Lycomings also come with three different engine mounting systems. The most common and modern is the DYNAFOCAL TYPE I which has a bolt attach angle of 30 degrees to a line that would parallel the crankshaft. The second most common is the CONICAL which has bolts which directly parallel the crankshaft. The third and least common is the DYNAFOCAL TYPE II which has a bolt angle of only 14 degrees to the crankshaft. Van's can supply mounts to accomodate any one of these engines. Another major consideration would also be that the engine have a mechanical fuel pump on the accessory housing. Many high wing aircraft do not use engine driven fuel pumps. If one of these engines is to be used on an RV then either a machining job is in order or a new accessory case must be located.
... A nearly complete list of these engines is included in the engine section (chapter 11) of the RV construction manual..."
I don't have my construction manual to hand, but you might.
Google is your friend...