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In the case of the Peacemaker and Russell's convertible TT, they will sink farther than you want them to. Catastrophically low actually. This is what prompted my research into valve material/hardness, etc. I worked with Ferrea to resolve a valve issue with their valvetrain and now all of their 300ZX valvetrains come with inconel valves for both intake and exhaust. The stainless valves they were using had the same problem that Nissan had but the results were much worse. To answer your question though, they shouldn't settle in any more than a few thousandths. IF you are using solid lifters, Tomei suggests 0.014" and 0.017" for intake and exhaust lash clearances, however, I think that is a bit excessive. When I was remachining the heads for the Peacemaker, we decided to go with 0.012" lash for both. The result was a much quieter valvetrain. I think Tomei may have been going by a non-lapped valve installation since lapping the valves prior to installation will keep them from sinking into the head at all, but not all machine shops lap the valves - they cut the seats, face the valves, trim the valvestem for proper height, and slam them together. You have to request them to be lapped otherwise they are just going to hammer them out as quickly as possible. The spring pressure isn't really a big factor once everything is seated. I would really suggest that your machinist hand-lap your valves and set the lash to 0.012".
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