.
...I agree with the above, that what you really need to do is to learn more about gearing, and what makes it work well to your own conditions and preferences.

More available cogs won't fix your problem, if cadence is your issue. If by "overpedalling" you mean too high a cadence, all you really need is maybe a larger big chainwheel, and maybe a longer chain to accommodate it. I did not look at your reference, but most Shimano cranks of that era came with 130 BCD chainrings, which are commonly available both new and used.

If by "overpedalling", you mean too low a cadence, thus having to push too hard on the pedals, work backward from that, looking for a smaller small ring in front. This ought to work out cheaper and easier than buying whatever it is you're looking at for 300 bucks Canadian. If the chainwheels on your current crank are riveted, not bolted to the arms, forget I said anything.