No, there is no real advantage or disadvantage with either positive or negative ground from an electrical standpoint. Either one works every bit as well as the other.
There have been some who try to find some advantage for one way or the other, but the plain and simple truth is that every device and every connection has a side that is connected to the positive terminal and one that is connected to the negative terminal and reversing them, in this application, provides no benefits at all. It is just how it was done back in those days, later they did the same thing, only with the negative grounded instead of the positive.
In these old tractors, the electrons don't care which direction they go.