Also remember that late 80's-early 90's was the transitional time for spacing going from 126 to 130. It was not unusual then for manufacturers to make frames in 128 spacing so that either type of hub OLD could be used. It was also a transitional time for manufacturers, Shimano included, and sometimes a bike that was supposed to get a 126 rear freehub instead got a next-level-up 130 spaced freehub with a 4.5mm spacer to correctly space out the cassette. That may be the case here. I've certainly been surprised from time to time, especially with some 7 speed tricolor bikes that came with an 8 speed 130 hub and a spacer.
Note that there were 7 speed Shimano freehubs during that period (e.g. 105 series 1051) and even earlier there were 5 and 6 speed Shimano freehubs on 600 and Dura Ace.
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Last edited by rccardr; 02-13-18 at 03:14 PM.