The 383(if it is a stock stroke 383 and not a 3.90 or 3.75 stroker motor) like to RPM a little higher than its bif brother 426 and 440 motor with the same heads, so I would probally get a set of 13x31x15 or a set of 12.25x31.25x15W. I have ran those same size tires on a Duster with a cross ram Hemi bracket motor and a different 440 cross ram bracket motor, those tires would hook either motor on marginal tracks The 14x32x15 are a lot cheaper used ( and use to be a very popular size for SS and tube chassis cars) so maybe that is why there on there still