587 heads

But with that rust on the seating surface it will need one............
It totally your call and if your cam don't require much much more spring pressure then stock, well, these are all plusses.

You could also just add leaded racing fuel to your tank, say a gal a tank full for a while or something like that to make them happy again.

Still recommend hardened seat. but there is more than one way to skin a cat.