Heyyyyyyyyyy!!!!!!!
I hope I am not too late. That Ryan cowl is just to nice to butcher up. The real plane used an inline engine in it and that is why it has a narrow cowl.
I put a gs engine on my Ryan and it is a thing of beauty. But if you put the gasser in that you are looking at it will be a nasty install.
I bought a RCS 1.40 with an inverted pitts muffler for my bird. I bought it specifically because of it's size and shape. I only have one hloe in my cowl that isn't for cooling and that is for the muffler pipe.
Go here and check it out.
http://www.rcshowcase.com/html/engines/rcs140.html
I am very happy with the way mine turned out and am going to test today. By the time I was done I only added 1/2oz weight to the tail.