A few months back I disassembled a NA6 cylinder head and sent Manley 3x OEM intake and exhaust valves to have them measured to spec and so they could manufacture a custom valve set for my 1990 Miata. They are using a design similar to their stainless race master pro-flo series that they have available for the NA8. I went with OEM diameter valves- not over sized.
The latest update is that they should have them ready to ship in about a month and I can add valves to the order if anyone out there is looking to refresh their NA6 cylinder head. Total cost should be right around $40 per valve shipped or $320 per set. If you are interested let me know and thanks!
