the porting is done to the cylinders, not the head.
the only valves in that motor are the reeds right in front
of the carbs.
there are a lot of guys that say they can port cylinders in most local
cities. truth is there are a few really good builders. they are all on here.
i would only let the guys i find on here do my porting. their work is tested
by BHQ members and proven to be really good.
FAST, Passion, and Herr, are the big names that come to mind, but there are others.
just do a search on porting their names will come up.......call them and
see who you like.