ORIGINAL: aspeed
I think you can get pressed in hardened seats for V8 motors.
Yep, when I converted my Chrysler 383 to run on LPG about 25 years ago I had steel inserts fitted to the heads. BTW, I wasn't quite correct earlier when I said the lead cushioned the impact of the valves. What the lead does is to put a barrier between the valve and seat to stop the micro-welding of the hot exhaust valve to the cast iron seat. This welding means that the next time the valve opens it tears a microscopic piece off the seat and this is what causes the recession over time. Obviously this only happens when the engine is running at high loads when the valve temp gets high enough.