Another “What is that for?” question

[68Gold/white]

When all the small blocks went to the larger journal cranks in 68, that hole behind the distributor was no longer made into the block. The big oil fill tube in the intake was not used much longer after that. The PCV in 68 and up went into the valve cover. If you have a 68 and up with the oil fill tube in the intake, it will have a cap that is not a breather type of cap. Emissions were tightening fast back then, the factory was try to get more control over all the pollution issues...

There's some exceptions the the above info, but you generally never saw valve covers with no holes in them after 67.