As mike says not many bridgestones around these days , great bikes , as regard the Dia of the bars, looking at your picture, looks like the shifters and brake levers you currently have fitted are shimano units and would assume unless the are overtigtned will be old school 25.4 mm, not heard of 25.8 ? ,You could always fold a piece of paper around the bars and mark at the join, then measure that if you don't have vernier calipers , the bar is it cracked or split to have the need to replace it?
Do you have any more photos too ?
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Too little time, so many trails !