We get calls about this all the time.
Heres the deal. generally if its a stock head and the chamber is really banged up and needs welding and 4 seats its not worth fixing. A good used head is cheaper.
If its a head that had a ton of money in it then its worth it.
Yes the head can be repaired and be just as reliable as new. Like Dwayne said, "if done right".
The proper press fit into the head is very critical as is the bore finish of the head after its bored to accept the seat.
Iron or bronze seats will work fine but bronze have qualities that are more desirable in some applications.
Bennifits of iron seats are long term durability and cost. bronze seats wont last 100,000 miles and are 3 times the cost.
Bronze seats dont work well in a diesel.
We make our own seats on a CNC lathe from certified solid Ampco 45 bar stock.
Heres some bennifits of bronze seats....
Bronze seats resist falling out better in aluminum heads because there expansion rate is closer to the aluminum head, where as iron expands much less and the iron seat looses its press fit when the head is very hot.
Bronze seats are softer and absorb the impact of the valve, better when it comes down on the seat. Thats very good for TI valves.
Bronze seats transfer the heat better from the valve to the aluminum head.
We weld and repair aluminum and Iron heads every day and there out there for years and years later.