Valve pocket/bowl hog tools....

I have a Souix set, and that what I do, because I don't have a Winona or equivalent guide and seat machine.
But I have to warn you, when you are using one of those slightly tapered stones, they tend to want to seize in the hole, kinda like ball joint stud tapers seize/ lock-up. Boom, the stone explodes. As long as you're wearing safety glasses you should be good, but the first time it happens don't be surprised. Just be patient and don't lean too hard on it.

Yep I have the same problem, I put a flat washer then a small spring and another washer under the stone and go at it easy, the spring really helps it from sucking down in.