73-87 Vs. 67-72 front springs..whats the diff???

[stevos67k20]

i was just wondering becuase all i'm hearing on these responses and stuff is "73-87 style" front springs. i will be purchasing new 6" front springs for my 67 k20 soon and i thought i ought to know as much as i can before i buy anything.
steve k.

 

[55Willy]

44" eye to eye for the 67-72 and 47" for the 73-91 springs