Jano, You make simple things sound so difficult, but everyone to their liking. You do understand that the point is not to grind even closely so much material away to match the shape of the efi head. That's overkill. People have even installed efi inlets to RST heads without doing anything, by accident, and have noticed nothing wrong. About matching the shapes, taking the head off and re-lapping the valves. You amuse me this time.
The real advantage of the adaptor plate, I find, is the extra thermal isolation of the inlet manifold. The downside is the moving of the manifold backwards. It will not clear many strutbraces and runners were longish to begin with.
In anycase all the pros and cons are minor and you do what makes you get a good nights sleep after doing it.