I am quite partial to that Ross flat six engine myself. I actually wonder if anyone actually used the engines in a airplane. I think the vast majority of the engines sold to modellers, even way back in the 1970's and 80's probably all wound up being displayed and not used.

They have a bit of a story about the engines that Lou Ross made here http://modelenginenews.org/drj/ross4.html

There are several varieties of the flat twin. I have seen rear exhaust and side exhast versions of that engine, and having the carb towards the rear and in the middle too.