Oh what the heck, I might as well put in my 2 cents.
I tell it the way I see it. I believe our R3 head design and valve arrangement isn't for performance but emission control. The same goes for the spark plug setup.
The combustion "squish" area is not designed for max performance. I would be willing to put my money into a new head design before cams, ram air and exhaust mods.
Sorry if I am stepping on someones toes, it's just where I would place my bet.
This engine should should be making a lot more power stock then it is now producing. Take a looked at the numbers for a tricked out old Ford Pinto dirt tracker. Old yes, but reasonable power for it size and time.
If I had my choice I would shorten the stroke, use smaller lighter high dome pistons and rods with a better non-emission cylinder head. I would raise the power band up for max HP as I am no longer interested in plowing fields.
If I can't do the above then I would resort to a water injected turbo vane style type of supercharger with inter cooler. I might even put some carbs on it. 8)
Remember........... "max power wet"
Chriss
NightRider