What about upping comperssion. I know you said you didnt want to get internal BUT removing the head doesnt seem so internal to me. Having bigger valves installed and possibly decking the head might be a way to go. Of course that is only if clearance will allow.
While the head is off you can also have it flow tested and tuned.
Then of course youd probably cross the line to getting bigger carbs. That might help now even without the above mods. Some discussion on the ratnet site has been going on about bigger carbs. At $1300 plus its costly but if you want to squeeze all the power out of it it seems a necessity.
