depends on where that 5/16" is. If it's to the sidewall it will rub in corners. If it's to the tread, well tread growth occurs. I have hte same issue with my 65 Cuda and a bit of judicial body work added a bit more (pull lower corner out by hand, trim excess metal , etc.).

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.