Hardened Valve Seats or Not?

If there is enough money in the budget, do it. You will sleep better at night knowing you won't have to worry about it. I did it for that very reason. Today's fuels are terrible and don't have all the good stuff these engines needed back when they were new. I am assuming that when you had the heads done years ago that they did a valve job. If that is so, then as stated earlier the induction hardening that was done by the factory has been tampered with. If cut deep enough depending on how well or poorly the hardening was done then the exhaust seats will be soft and ultimately fail.