How deep/large is the hardening surface on 425s heads ?

If you cut them out to 2.14/1.81 valves are you still on hardened surface ?

Can I port with templates first and then cut to bigger valves ?

If you go to that valve size they will install new valve seats. The porting templates are made for standard valve size. You could port with the templates, then have your larger seats installed, then hog the bowls out a bit to take advantage of the larger seat diameter.

I just had a set of 452's done by Dwayne Porter , they were cut for the bigger valves and I was going to have hard seats installed because it's goingto be a street engine that will see alot of miles. Dwayne said it was still hard and did not need new seats installed in his opinion ...

your heads may be different ...