Torque arms were a good solution in the 1970s, and were a big upgrade from leaf spring rear suspensions. This type of suspension was OEM on a few cars designed and built in that era, like the
1975-80 Chevy Monza and a Torque Arm even crept into the 1980s in the
3rd generation F-body - who's rear suspension lasted virtually unchanged from 1982 allllll the way into the 2002 model year.
3rd generation F-body - 1985 Camaro - with the OEM torque arm/pahnard rod rear suspension
The Fox Mustang was a popular candidate for aftermarket Torque Arm conversions, as the "quadra-shock" and opposed 4-link rear suspension this car used from 1979-2004 was abysmal and also had it's beginnings in the 1977 Ford Fairmont. That rear suspension was SO BAD that the 1970s-era Torque Arm solution was still a significant improvement, as it removed inherent bind in the factory 4 link arms and reduced the need for 4 shock absorbers back there.
Torque arm + watts link added to S197 Mustang
I have personally installed TA suspensions on dozens of SN95 and Fox Mustangs, and have owned and raced in many of those as well as 6 examples of 3rd and 4th gen F-bodies with the OEM TA rear. There are drawbacks to a TA suspension, mostly in braking. Axle hop under braking was so bad in the F-bodies that I've seen cars shatter Tremec T56 transmissions... hop-hop-hop-BOOM! Gears and transmission case parts explode. The rear shock valving is critical on these TA equipped cars, as is the bushing material.
I've raced on track in our 2011 Mustang against some of the fastest W2W F-bodies in the country and I can ALWAYS outbrake them with the OEM-based S197 3-link rear suspension. Sure, the factory S197 rear suspension set-up isn't perfect, but its a damn sight better than some torque arm mess. With a few changes it is very good, for a solid axle RWD car.
With a lowered ride height we always alter either the upper or lower arms from stock by adding adjustable lengths to these arms - normally the LCAs. And we add relocation brackets. We prefer Whiteline rear LCA arms with their elastomer ends, because they don't bind AND they don't clunk like spherical arms tend to do QUICKLY after being installed. We've removed too many metal spherical ended LCAs to count and replaced them with the Whiteline arms. I've not seen the perfect UCA replacement yet so I encourage most folks to LEAVE THE STOCK UCA IN PLACE. There are much better places to look for speed than this spot, as the aftermarket solutions almost always add LOTS of noise, or bind, or both.
The only time I'd think about a torque arm on an S197 is if I was racing in one of two SCCA Solo classes with their super restrictive rule sets. No, the real term is "retarded rules wording". They don't allow adjustable LCAs or LCA relocation brackets in ESP or STU classes, which will screw up the rear geometry when you lower one of those cars. Because they don't know how to write rules or understand common suspension fixes to solid axle RWD cars. Ignorance is bliss. To fix the issues in these cars WITHOUT simple adjustable LCAs and brackets (ie: with retarded rules) you have to get fairly drastic, and a TA is one of the only legal solutions for
those 2 small SCCA classes. And I'd only do it in a dedicated race car S197 for one of those 2 classes. This "torque arm fix" then applies to about 8 people on the planet, so ... probably not anyone reading THIS POST.
S197 with Whiteline LCAs + brackets + Watts = WORKS and is QUIET with no downsides
As a suspension designer/mechanical engineer and competitor, I've studied the torque arm solutions offered for the S197 and found them all to be "a solution for a problem that doesn't exist" on this chassis. I could safely say that almost everyone making a TA solution for the S197 pretty much is doing it because they used to make TAs for the Fox and SN95 Mustang chassis. Lots of clunks and bangs and lack of ground clearance and worse braking. Half of the crap offered in this industry is just a "legacy solution for a prior chassis" applied to a new chassis. As a racer, though, if I felt that a torque arm would make my car faster, it would be on there.
It isn't, because it won't.