Can you take me a photo of the part number on the NF head?
Trying to see if its in the same family as the KV, if so then itll respond very much as per Richards KV head.
Cam upgrade to the same spec as Mr shrick is going to help also.
Exhaust - stands a chance of helping as does cat removal, but only if its restrictive in the first instance....come to think of it, i could probably check that by putting it on the tester and see what the flow loss came to.