There is a mark on the inlet valve seat of the old engine. If it isn't a bit of dirt, it's a crack. That could be a problem, since it will propagate to the area that contacts the valve-head, and cause a leak.
The part of the seat that contacts the valve head should be 0.8 mm wide for a new engine, with a maximum of 2.0 mm as the service limit for used engines. I don't like to see them much more than 1.2 mm: it becomes difficult to maintain even seating all the way around. Note that by the time the seat gets to be 2 mm wide, there is quite deep wear to the valve head, and the valve has to be replaced. Remember, the inlet valve seat insert is not hard, but the exhaust one is. Re-cutting the exhaust seat calls for a diamond cutter. Don't make my mistake and try to re-cut one with a standard cutter, or you'll have to resharpen the cutter tooth by tooth, as I did.
