Should be a model number information on either the back or inside the head near the control boards. As far as I have seen "Skee Roll" are the older model D and model E "skee ball" machines, made by Philadelphia Toboggan Company.. which later changed to become "Skee-Ball Inc" (so they are actually true "skee ball" machines but prior to the company changing the wording on the marquee). You will likely see "Model 77" or "Model 78", etc if you find a plaque with the model information on it inside or on the backside of your machine. The model number seems to be the year it was built, but the control board will then be a Model D or Model E unit.
We have had some machines with marquees that say "Skee Roll" and others that say "Skee Ball" -- I'm not sure how long they used the "Skee Roll" marquee. Deltronics made the electronics in the machines from Model D thru the Model H alleys.