New guides, bronze manganese for tighter valve fit, improved Viton seals, and a valve spring upgrade (lightweight duals tool steel retainers 150# seat 400# open), Serdi valve job, and CC chambers would be the essentials, in my opinion.
Airflow improvements would be appropriate with the added compression and a longer cam to increase performance.
Personally, on my CVO 110, I didn't care about more power, but I went into the motor with a plan that in two weekend days, the work had to be completed, and this is precisely what I did. I wanted to address the CVO 110 known issues only in the interest of reliability. I changed to Timken cam bearings, Morel lifters, Smiths pushrods, and an Andrews 54 cam. It has all my original torque, a quiet valve train, and ten added horsepower. Not in the time budget to port the heads. I am happy with it for the little time I get to ride.