you won't find much for production number breakdowns beyond the number of light, medium, heavy trucks, they didn't keep records back then of options .... in 58 there were about 158,000 trucks built under 6,000 GVW - in 59 there were about 196,000 so you could say 58's
were "less common", but really they're equally uncommon, how many of either in your town? in Germany? in Europe?
because the big window was an option it was probably rarer when they were new, but I think more of them have survived because more people prefer them, so based on what's around today, the small window would be rarer ... why not keep both?

Bill