Only with some heads can you do the above!!!! + The seal is not great if you can!

If the head is off you could grind the ports yourself

But that would involve taking the valves out so you dont end up with loads of metal in the seats. Then having to lap them back in.

Whats the chances of grinding all the ports exactly the same??

For the small amount it costs for an adaptor plate i dont think its worth taking the head off or trying to grind the shapes yourself IMO