Peanut plug head. Crack in valve seat.

Head off a '76 Dodge Aspen wagon.
Burnt exhaust valves in #3 & #5. Crack in valve seat in #5.
Got another head. Unknown origin. Crack in #2 exhaust seat.
Is cracked exhaust seats common in peanut plug heads? Locals here say have never heard of one cracking.
What do you say ?