Those inserts need to be snug... as in putting them in dry ice or freezer and the head warmed up and be a snug fit while pressing them in quick... and that 6 punched seat, the head should have been built up and cut down before putting that seat in.

 Sorry, but thats shoddy work.

That head for the most part is scrap with the "staking" of the exhaust seats into place. In automobiles this creates hot spots which usually show up as cracks through the seat and non sealing valves as a result. 

The head is salvageable if a rare item. The existing seats and surrounding area would need "cored", and another cast iron insert shrink fitted into it. Not all automotive machine shops have that capacity but one that builds high performance, ($$$) engines may. I can't say these days for sure. For a short time in the late 1970's I worked a shop that could do that work and you'd never have a problem with it. Valve recession was a big thing in those days as unleaded gasoline was not in full force yet, and regular leaded was still routinely available, but it was rapidly becoming understood what the lack of lead in gasoline was doing to non hardened valve seats. 

Use your best judgement it's your project.