The only finish difference between the HP(M28) and the .357 Mag(M27) is that the latter has mirror polished metal prior to bluing, the M28 does not. The reason for my suggestion of bluing the cylinder only is to avoid rounding of corners and messing up the sharpness of markings and sideplate of the frame which does not look that bad. I don't think the blued cylinder will be that badly mismatched with the frame afterward and at worst will look much better than it does now. Alternatively, the entire gun could be given the beadblast treatment (using very fine media) and then hot blued. I have done that on numerous guns and it looks very good.