changing sock pattern

[Sewist]

I'm knitting socks but need to change the size - for the men, I usually cast on 64, size 3/3.25 needle and want to size it down to a cast on of 60 stitches. How do I calculate the rest of the pattern - i.e., heel flap, gusset, etc.? Is there a special formula for this? I've checked my knitting books, but nothing there

Thanks