Hi,
Yes, the 50 Sport, 60 Sport and all non oil injection BS90 models came with the same plastic side covers. The only difference was the enamel emblem on each side. Also. the oil injection 90s and the 100 Sport used the same left hand cover, but had a different right hand cover to allow for the oil tank.
There were some identical left hand metal side covers made (I found one to use on my early 90), but I'm not sure which model they were for. (I would guess they were probably used on late oil injection 90s and the 100 Sport).
Hope that solves your problem.
Graham