1972 dart alternator pulley shaft question

figured i'd ask , just in case . 1972 dart 318 , stock . daily driver . alternator went . i had one sitting around here that some cool old school mopar man gave me years ago . that was tested good for my application , at a autozone ,recently . and matches up almost perfectly , but when i went to put the belt on , the belt was harder to put on . i noticed the pulley where the belt goes in was a bit larger than the old one . the belt fit great and is not too tight . but i was just wondering . can the diameter of the pulley cause any difference ? anything to worry about ? it's already on and its too damn hot to start over . do i need to swap the pulleys ? have i been out in the heat too long ?