Your Grizzly was made in the '70's--hard to tell what year,though.Bear started the "K" serial no.'s in 1970.You'll need a 58" AMO string-actual string length will be about 54".Use dacron(B50 or B500)and not a fastflight string.The 45X# is 45# at 28".The X means that it didn't make weight.I just forget if it means under 45# or over 45#