516 head question

I did a compression test on my 361 and found one low cylinder, so I am getting ready to have the original 516 heads redone. Nothing fancy, perhaps change out the 1.60 exhaust valves for 1.74's. I was thinking just a 3 angle valve and a plunge cut, and then just blending out any ridges left behind. I have been doing some reading indicating you have to be careful or you can get into water on these heads. I am enclosing a picture I found showing the kind of plunge cut I am talking about. There seems to be quite a hump in the stock exhaust port right next to the intake valve. Is this where they are thin, and should I be concerned about the plunge cut?

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how did you make out with the 516's?
I am in the same boat rebuilding 516's with 1.74 and want to use 911 springs.
Cant find much help on particulars.