There are several manufacturers making multicylinder 4 stroke gasoline burning engines for r/c. The most popular 5 cylinder radial which I believe is in
most of the radial powered birds at that meet is made by MOKI from Hungary. They have also recently released a 7 cylinder as well.
The P51 Galloping Ghost reno racer replica has a 3 cylinder inline 4 stroke gas engine made by KOLM engines from Germany.
All these multicylinder engines sound awesome live.
You just need to somehow convince the Misses about the $$$