My info says for a 1978 the front coil is 9.0 tall [compressed] x 3.5 dia and a .57 wire dia. The free length not listed. Rate is listed as 300#/in or 350#/in HD.
This info is in the MVMA Specs listed on mustangii.net
There was only the one set of dimensions even though they listed 2 rates
Don't know if this helps but its the best I can do.