What size countersunk screws for Audio Research Ref3

I would contact ARC.   See if they can send you some.  Countersunk screws have either 80° or 100° bevel.  A 100° bevel in a 80° will stick out and a 80° will not be flush in a 100° bevel.   Best to get the O.E.M. screws

If ARC doesn't pick up use the SAE since it's the states and most likely all will be well.

I misplaced mine, got them from ARC.