What for tool do you have that will allow you to go into the guide in the engine to determine that? As a rule of thumb, if you can wiggle the valve in the guide back and forth to where it is excessive, it needs to be replaced. also if the valve does a slide to one side or the other when you close it to the seat, it is in need of replacement.
The tighter the better to the point of having it tight enough to seize causing the valve to stick open. I used a reamer that was .0005 bigger than the valve stem and then honed with a ball hone. When installing the valve use anti-seize compound. I never had one stick using that method. -- Chuck
I like to run the valve to guide clearance much tighter than that. Keep in mind that the exhaust valve will get very hot, while the intake valve is constantly being bathed in cold alcohol.
If you do a little looking around, you can find small bore gauges available on ebay and through machine shop and equipment liquidation auctions.
Valve seal is important no matter what the class.