I've rebuilt several 230's and 250's with no problems, and no special attention was given to the valve seats. The hard seats and/or stainless exhaust valves are mostly needed for high performance or heavy duty applications. A good 3-angle valve job with the proper seat width will do more to assure a long-lasting cylinder head job than doing a lot of exotic machining. A good rule of thumb for exhaust valve seat width is .090", or 3/32" if you're using fractional measurements.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!