I have an attachment for my Black & Decker valve grinder that is used to put a radius back onto the rocker tips, using the grinding wheel that also squares off the top of a worn valve stem, with a stream of grinding coolant running on the operation. Some people argue that it's not perfectly accurate, but any method that approximates the right contour on all the rockers is better than going after them freehand on a belt sander. Most oldtime machine shops will have the same accessory on their valve grinding equipment if they have been doing good quality work- - - -the trick is finding an old geezer like me who knows how to use it. If he doesn't have any luck elsewhere, send 'em to me!
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!