Click on the engine choice tab, this is what they say, the omission of the RV12 stuff is at several such places:
Introduction - Powerplant Choices
RV aircraft are designed to use Lycoming aircraft engines.
The RV-4 and RV-6/6A use 150/160 hp 0-320 or 180 hp 0-360 engines.
The RV-7/7A and RV-8/8A can accommodate O-320, O-360 or angle valve
IO-360 (200 hp) engines. The RV-9/9A is suitable for Lycoming engines in the 118 hp to 160 hp range. The engine used in the 4-place RV-10 is the Lycoming IO-540D4A5 rated at 260 hp. Van's recommendation for the 4 place includes any of the parallel valve 540's which are available from 235hp on up to the 260hp version. These engines are the most readily available, affordable, and reliable of the possible choices. Other aircraft engines of similar configuration, weight and power might possibly be used, but only the Lycoming will fit the mounts and cowls supplied with our kits.