qasimshah
I respect your affection for the Mustang, but sadly it was never accepted as a "Musclecar" it was and always will be classified as a PONY car, because that is the segment to which its size( physical, not engine) relegated it. Even here it has the company of the Z 28 Camaro and Pontiac Trans Am to name two others.
The musclecar breed is virtually ruled by the large full size cars with the 426 HEMI with the odd Chevy 427 0r 454 thrown in.
No major american publication had the Mustang on their top 10 "musclecar" list. This list was always dominated by the HEMI's.
The US produced the greatest musclecars in the era you are refering to notably the Chevelle SS 454, the Pontiac GTO, the Plymouth Super Bee, Road Runner and the mighty 440 Six Pac to name a few.