Gee, better hope the Harley bashers here don't read your post because they'll think you're lying. They all think a Harley is incapable of making that kind of power. For their own self confidence, maybe they shouldn't read it because otherwise they might not be able to sleep tonight.
I don't know about your bike, but the older engines always benefited from a carb and exhaust with better flow characteristics. Since you've pretty well taken care of that, what about the camshafts? On the older engines, that was the next step up for more serious hp with the final step being a little head porting and polishing. However, with the head work I don't think the $ would equal the few extra ponies gained. If you were to do some serious valve work (bigger ones), then you would need a considerably more radical cam and you'd almost surely shift the hp potential farther up the rpm scale and lose low rpm grunt. For a dragster it might be ok, but for a street bike, I'd pass on that part. Just remember that dyno numbers aren't everything and don't relate to tractibility.