replacement of balances

I have 8 windows, of which 7 of the balances are in need of replacement. These windows were installed in 1987 and are in excellent condition with the exception of the balances on some of the windows. Two questions ~ first, there are three different window widths 2 are 44", 4 are 40" and 2 are 38" -all are 58" high. Are the balances the same or interchangeable regardless of the window width. Second question - it appears they are installed with what appears to be a staple type of nail. Can screws be used to fasten (I haven't watched the video)tutorial. Thank you.