I looked at the Tower site, and they sell 3 versions of the OS 70 fourstroke. The original is about $190, the version II is about $210, and the Ultimate is about $300.

If I was to be choosing one, I would think about whether I needed a pump or not. My fourstrokes are usually mounted with the carburetor about mid-tank height, so I don't need pumps. The extra $$ would probably push me toward one of the others, but you may have reasons to use the pumped version. For instance, the pumped Ultimate is cited as having measurements a bit shorter than the earlier version. If you had a particular cowl measurement that might enclose the Ultimate but not the earlier version, that might be the decision maker.

Good luck,
Dave Olson