The International eveolved quite a bit over the years, It could have side side, centre-pull or cantilever brakes.

As previously suggested, clean the rims and upgade to some good pads and cable housing. I'd also change the cables themselves. It's not unusual for manufacturers to scrimp by using light gauge cables, which results in spongy brakes. If they are cantilever brakes, as per Randy's pics, improperly set pads can severely alter performance, though after this amount of time, they'd normally have conformed to the rim.

If there is sufficient frame clearances, recommended safe maximum tire widths are based on the rim width and flange style. Standard rims will safely accommodate tires up to 2x times the rim width (measured between the inside of the rim flanges). Rims with hooked-edges on the inside of the flanges extend the maximum tire width up to 2.25 times the rim width.