Hardened Valve Seats or Not?

If you had not done the heads already i would say add the hardened exh seats.
My 340 ran 12 years on non hardened seats with out a problem. It got a gal of leaded racing fuel every time i raced it. which was a couple times a mouth in the summer, unleaded all the rest of the time.

I replaced my 360 heads for a set of X heads and had them install hardened seats in it.

I have been told (don't know how true it is but.....) the first 1000 miles is the most crucial time for the lead treatment, that the lead don't go a way and is really not necessary after that except in extream condition such as a motor home or truck trailer combo.

street car, drag racing, don't put enough heat/time on the valve to cause the erosion.