If it's got stellite/sodium-filled valves at present, you may be able to grind them (big savings over new valves).
These oem valves are good for high heat....the sodium (inside the valve) turns to liquid when the valve reaches operating temp and carries heat (from the head) to the cooler part of the valve (near the guide). Big bucks for new ones.....I paid almost $30 each for sodium filled valves in my old Mini.
Not sure about the other choices, but you'd want to check and see if they're OK for unleaded gas