it isn't really the hangers you measure.
measure the front segment of the leaf springs and see what they actually are.
if they are correct for a b-body, then your hangers are suspect.
if they are short, you know you have the right hangers, just the wrong springs.

early b- 21 x 35
66 and up b- 22 x 36
e-body 22 x 35
r,f,m and J 24 x 34