I don't think that there is a simple answer to whether hardened seats are desirable or not. There are a lot of variables to consider. What is the quality of the gas in your area? What kind of spring pressure do you have? Cruising operation? WOT operation? Unless you know the effects of all the variables in your area, I'd go with the seats. Least risk option.

One variable that I have not seen mentioned is the casting quality itself. When it comes to blocks, I have had early 440 blocks that were hard as Hillary's heart, and late 70's blocks that machined like aluminum(A bit of exaggeration)
It would seem unlikely that heads were cast much different. Some may be hard enough to work fine, others not. I know I have seen several 340 X heads that the valves were so sunk in you would need a big roller just to open the exhausts and that a'int no exageration! I would put the hard seats in, it is cheaper in the long run, both in race gas and peace of mind!

The cheap street 360 I have posted in the Race/ Engine section had 15,000 miles on the factory valves and seats since the valve job had been done. I pulled them off to test a set of stock RPM heads recently.
The exhaust valves are sunk so far in the heads its hard to believe it ran as good as it did. And the E heads averaged only 5 horsepower and 5 lbs ft more. So I can believe guys can see little change in performance even if the seats are beat in a mild engine.
This engine was in a motorhome before and saw towing duty,so the extra stress may have helped valve recession along. I used pump gas and on occasion a lead replacement additive,but not at every fill.
My current 440 tow vehicle got hardened seats added,just as insurance.
Keith

Man it's sure sounding like I should do it right the first time (which is what I am always preaching on here ) with some GOOD seats on the ex side. Thanks guys for all the info/suggestions/recommendations & time you took to post on this issue to enlighten me

I've commented on this subject many times, if you wanna do the rebuild once put in the seat inserts it is the only way to do it. Once the old valve seat areas get beat out and get into dead soft cast iron it's over. Engines used for towing or heavy vehicles causes extreme heat on the exhaust side and super heat the seat area because it doesn't transfer heat into the head fast enough.

MLR426

Performance Plus Cylinder Head
Odin, IL

First, I have driven my '64Dog for around 100K miles and always used unleaded gas, as it was the only kind of gas available. I have never had the exhaust valves close the clearance with my mechanical lifters. SO, from my own personal experience I have not had seats destroyed. That's with stock cam stock springs.

HOWEVER,

RR has said he's installing larger exhaust valves. That means the exhaust seat areas will have machine work done on them to fit the larger valves.

It only makes sense, as the head is already in the machine shop with work being done to the exhaust seats, to install hardened exhaust seats at the same time. It won't add a lot to the total bill and it should provide trouble-free service no matter how big a spring he puts on the valve.

R.