225 Porting

I have a peanut head most of the way done, at least as far as I dare... considering how many who know more than me talk about hitting water jackets. mostly, I cleaned up right under the valve seat area, and cleaning up the big lumps at the top of the valve guide area (meaning, as head sits on bench for the work I am doing, I know is upside down from being on engine.... but gotta reference somehow) have 2 cylinders' worth to go. I see that you opened up the exhaust valve side of chamber too. I, too, want to do the o/s valves. there's another member that is on both here and on the /6.org site that I have talked to about "finishing it up" for me, as he has (at least access to) a flow bench. I think he actually has his own. Mine (at least this engine) will never be a race engine.... rather, it's gonna be a truck engine. but the flow bench thing is more for giggles than anything. I think that in my case either O/S valves and/or seat inserts are gonna be a must to be able to use this head.... had a few "oops's with the burr bit accidentally meeting existing valve seats.
I have a porting question for those who have done more of it than me (probably most here if I had to guess) When going to O/S valves is it mandatory to replace the seats with seat inserts?
I mean, I know there was a point in the early to mid 70s, where they started hardening the seat areas, when leaded gas began to be "watered down" so to speak, as lead in gas started going away. I'm thinking that if the virgin head material is simply ground away to fit O/S valves, that the hardened layer will be ground away, and valvs will sink into the head. I'm looking for 100K+ mile durability out of this engine, 3 season daily driver kind of thing. NOT a "weekend warrior" that just goes to swaps and car shows a few times a year.