8 or 18 or et37

I have a spare set of wheels that I know fit the ML320/W163 as it was delivered with them on (happy). 255/55/18 However I'm now running 275/55/17 on a set of MB appropriate alloys. Question, whilst restoring the 8/18/h2/et37; what tyres could be fitted? Having lived with 275 I do not...