If the pads reach then great. If they are REALLY close you can file or dremel the slot a little lower. This assumes caliper brakes of some form. If they are cantilever brakes then you're in for a rough time since I doubt you'll get the pads to go that low. And if you did the brakes would become too easy to end up self energizing due to the pad being so close to the pivot point in the horizontal direction. But the older bikes more frequently used caliper brakes so I'm going to assume that is what you have.

That being the case you WILL notice a big increase in the lever pressure needed to stop effectively. You can switch to Koolstop salmon (Scott Matthaser) pads for more bite. But by far the best way is to spring for a new set of long reach Tektro dual pivot calipers Those are FAR nicer than extended to the max single pivot calipers.