surly steamrollers should take more that 48t, I ride one with 49t , 8bar track cranks with HT2 bb (I believe these are rebranded andel or something something taiwan) and there's plenty of space left. hope the pic helps a little
edit:sorry its just a 46t in the picture
Yeah, cheers. Tester mentioned those. They look interesting and might be a solution if I can't get the Shimano cranks working like I want.