The reason the OTC (
OK, I reread the first page. Is it true the SD was a shortened full size car housing down to Camaro width?
Yes, and the reason they did this (for SCCA road racing purposes) was to use the LARGER axles, and LARGER axle bearings for the severe duty application.
Shortening a full size differential is a potential route to go, BUT... you'd need the special axles with larger bearings to complete the rear end. The biggest reason cars quit using the 'Service Duty' rear was the non-availablity of the axles in the early '70's, and even before they were taken off the books, they were VERY expensive to buy.
One of my friends who ran TransAm (Robert A Christiansen) bought a new '69 Z28 and drove it from the showroom in Dec'68 to his shop and immediately began removing parts and converting it to SCCA specs. Everything I know/remember about the Service Duty rear end came from him in the 70's when I assisted a little on his cars, and he helped me rebuild the engine in my '69 Z28. I have notes from him re all the other differences in the SD rear vs the JL8 rear (and there are several). Even in Dec '68, he had to go thru Vince Piggins himself to get a Service Duty rear (I have that rear end now). Bob used the rear in his '69 Z28 racer in T/A racing, and then in IMSA GT racing until the axles became unobtainium; I have the last two sets of axles that Bob used in that car. When the '69 Z28 body became 'too old' for IMSA, he bought a '73?Camaro body and moved most of the HD parts he had to that car (and sold the '69 to some local SCCA racers in the Atlanta area - I later purchased the rear end, axles, and 2 sets of the Magnesium wheels from that car from those fellas in the late 70's, after they had sold the car to a doctor-racer in the Chattanooga area. A few years ago, I loaned one of the axles to a fella Camaro owner who had an axle mfg MAKE some duplicates of the SD axles, and he made his own SD rear by cutting down a FS differential.
PS. If you wanted to make your own 4-wheel disk brake rear (JL8 clone), you could do that from the 12-bolt std rear, and add the disk brakes and other incidentals necessary. I think all those parts are available, but you would not have a 'numbers' JL8, but it would stop/look just the same. I also have an NOS extra pair of the caliper brackets and backing plates for the JL8 if anyone is interested.
