Even on a four stroke I would only recommend the most basic of porting to the average individual. Any heavy porting and a person is more likely to screw up the flow rather than improve it. And don't even cosider sending it to a shop without a flowbench.
Stick to matching the intake port, cleaning off casting flash, smoothing off the ceiling a bit, cleaning up around the valve guide...any reshaping of the port should be left to a professional.
And on almost all vintage four stroke japanese bikes....forget doing any porting unless you increase valve size...that's almost always the limiting factor on these engines. Sure you don't want your intake flange and head flange 1/4" off...or a big piece of casting slag hanging in the port....but for the most part, unless you get bigger valves it's a waste of time.
JohnnyB