Ok... now you're really poking my interest....
A Moki 400 Radial... or a Kolm 3 cyl inline (e.g. Galloping Ghost).
Both magic beasts
I'll see if I can get some mock-up pics of where I'd like the 180 to sit in the BF 109.
...and you don't need big four-bangers to go seriously fast. This humble little Rotax 256 Twin 2-stroker flogged a fair few bikes (and V8's) in it's day...
BJ
