I need help with a new bought motorcycle. I have a 1987 GSXR 750 and am trying to find new tires.?

The bike is spec‘d with a 140/70-18 in the rear and it seems I am only able to locate tires in the 160/60 size. Will these work on my bike? Also, what would be the difference in riding with a bias-ply tire instead of a radial tire?