Centres
Assuming that you are working on a Boosted engine, 114 degree centres will work fine. Be sure to set your valves to the tight side of the factory specs and follow Powderlight Dave's thread listed in "sticky" as a guideline for setting cam timing. Other threads cover this on TY4stroke forum as well.
As for porting your head, probably a waste of time and money. Definitely get a proper valve job done, sealing is critical, but porting is "not" when Boosted. There are only two shops in the US that are showing only marginal gains in all out boosted applications when porting Yamaha heads. These shops are installing larger valves which is really where the flow gains are coming from, not from gouging out the ports. Lots of people will disagree and this is my opinion, do the research, call and talk to the guys that are going fast on the Asphalt, or have a Superflow Dyno to back up their claims. Head porting can have some benefits when naturally aspirated, however, if done in a shop without a flow bench, by someone that is not truly experienced, chances are they will have hurt the flow volume numbers.
Cheers
