Personally, I've used successfully the standard class of fit. Despite that they were often free/extremely cheap, I reason that despite any additional clearance, the wear in the crankcase journals would offset the need for additional clearance.
So, in a roundabout way, putting the cart before the horse, I believe that C3 is the appropriate class in any case, but can't verify that. It is in Sticky's book.....I think.
What I said about old crankcase journals becoming slacker fit still stands & I think C3 appropriate for fresh cases, but I reckon you'll be fine.
(Sorry about the lengthy reply but I do try to make matters clear

)