Dial question for Omega 2857/2856-3 case with 501 Movement

Hi. I have a Omega 2857/2856-3 case and a 501 movement. I need to find a dial and I'm not sure what size fits. Seems like most 501 dials are 27.5 mm but the inside case diameter is roughly 30.4 mm. Does anyone with a similar setup know what diameter dial this case needs? Thanks for the help.