Pretty sure it's a '78 and was surprised to find 6 cogs. It has so few miles, I figure it came like this from the shop. The chain sometimes will hit the seat stay on its way up and off the 13 tooth small cog. I might be the only person who shifted to that cog ever as the derailleur wouldn't reach it till I loosened the limit screw. With wheel removed, drop outs are spaced 124mm. I expected 120. Should I try moving the drop outs to spec and go back to what I believe should be a five speed?