I don't think any of these cars had a factory underhood starter button. so as to what the one you have is for, or what it does....you got me!

who knows what the previous owners of your car did.

could be a starter button to bump the starter while running the valves on a solid cam? if so, it'll just bump the starter over, it won't actually start the car and let it run. (unless you have the key in the "run" position, in which case, bumping the starter under the hood WILL make it run! )