Not trying to be difficult here, but I disagree.
I'm not sure where that reference came from, but whomever wrote it is mistaking a Posi-Trac for a Spooler/Locker.
Also, he is referencing a Ford which was a Trac-Lok, not a Posi-Trac.
Way back in the 1970's I worked as a Machinist for a company that specialized in Racing modifications for (mostly) drag racing.
One of the biggest selling products we made was a kit to convert a Posi-Trac to a Spooler/Locker, very useful on a Drag strip.
The kit did the same as welding up the spiders, but was something people that didn't know how to weld proper could use.
Back then, every racer had an ARC welder and
thought they knew how to use it but for some unknown (to them) reason, they kept blowing up rear ends..go figure.
We use to have a booth at the local drag strip (Fremont Raceway) and we would show car owners the benefits of our Posi-Trac Converter Kits most every weekend.
Since the powers at be have closed most drags strips, read the Wiki links or any of the off-road forums as there's a lot of talk still going on there about the subject.
(The difference between a Spooler and a Locker in the product we sold was you could manually unlock a locker and drive the car on the street whereas a Spooler was a permanent 'Race Only' mod.)
http://dodgeforum.com/forum/1st-gen-dakota/178531-home-made-posi-trac.html
http://www.countrybynet.com/forums/vehicles-etc/24832-can-rear-end-converted-posi-track.html
http://en.wikipedia.org/wiki/Limited_slip_differential
From the Wiki: Factory names
In the 1950s and 1960s many manufacturers began to apply brand names to their LSD units.
Packard pioneered the LSD under the brand name "Twin Traction" in 1956, becoming one of the first manufacturers.
Other factory names for LSDs include:
Alfa Romeo: Q2
American Motors: Twin-Grip
Buick: Positive Traction
Chevrolet/GMC trucks (after 1973): Gov-Lock and Positraction
Chrysler: Sure Grip
Dana Corporation:Trak-Lok or Powr-Lok
Ferrari: E-Diff
Fiat: Viscodrive
Ford: Equa-Lock and Traction-Lok
International: Trak-Lok or Powr-Lok
Jeep: Trac-Lok (clutch-type mechanical), Tru-Lok (gear-type mechanical), and Vari-Lok (gerotor pump)
Oldsmobile: Anti-Spin
Pontiac: Safe-T-Track
Porsche: PSD (electro-hydraulic mechanical)
Saab: Saab XWD eLSD
Studebaker-Packard Corporation: Twin Traction
TVR: Hydratrak