Competition suspension should also have staggered rear shocks.
From all my research and related documentation, staggered shocks were a separate item from the competition suspension.
So from what I understand, staggered shocks were required on all 72 & 73 4-V (Q-code) Mustangs. Again - competition suspension was a separate item. My convertible is a 72 Q 4 speed and has Competition Suspension listed on invoice and it has staggered shocks. Very unmolested car. There have been discussions on whether the 4-speed 'drove' the installation of the staggered shocks or the 4-V "Q code" motor...
As for 1971 models - it gets tricky.
It is TRUE that all Boss 351s came with the staggered shocks, BUT it was not a part of the competition Suspension Package.
In 1971, all Mach 1s, Boss 351s, 429CJ and 429CJ-R cars received the Competition Suspension as standard equipment, however only the Boss 351 received the staggered shocks as standard equipment.
From the 1971 Mustang Facts Book rev. 2/15/71
http://www.7173mustangs.com/thread-1971-ford-mustang-facts-book
"An optional COMPETITION SUSPENSION is available
with all models except those with the 250-c.i.d. engine.
The competition suspension includes heavy-duty front and rear
springs, heavy-duty front and rear shock absorbers, heavyduty
front stabilizer bar and rear stabilizer bar with 351-
c.i.d. 4v and up. The competition suspension is standard
on the Mach I, Boss 351 and with 429-c.i.d. CJ or CJ-R
engines.
Mustangs will again be equipped with staggered rear
shock absorbers in 1971. Staggered rear shocks (the right is mounted in front of the axle; the left behind it) counteract
wheel hop and increase traction during acceleration
and braking. Staggered shocks also provide improved rear
axle control with higher output engines and are standard
with all 351 4v, 351 4v HO and 429 CJ, CJ-R engines."
Some M code '71 cars were hit and miss for the staggered rear shocks. That (for me) is the tricky part.
Learning all the time!
Ray