I can't explain why Opel did the two-part drive shaft/torque tube deal, but, as for replacing the torque tube, as long as you get the geometery of the driveshaft correct, I don't see why it (torque tube) would have to be duplicated. BTW, where in SC are you at/from? I'm from Georgetown, on the coast.
I'm in the Columbia area. I work in Blythewood, and live in Swansea. Georgetown is near Charleston, isn't it?
The torque tube thing is bothering me because I'm in the early stages of an engine conversion, and I know the stock rear end will not handle the 200+ hp and 200+ ft/lbs. torque that I will have on tap.
The torque tube is a suspension locating link. It prevents the axle from rotating, and creates a 'pivot' point at the front of the torque tube area, acting as a supension arm. If you install an alternate rear axle, you will need to either add one or two more links to the top side of the differential, the lower links are not enough to prevent the axle from rotating.
If you add one or two links to the top of the differential, could you attach one at each end of the axle housing (near the existing lower arms) and fabricate new attachment points near the ones for the lower arms? Or is there a preferred location elsewhere? I need to keep this simple.
It won't be so simple. You will have minimal room to attach the links without cutting the rear floor of the car. Travis put a Toyota rear axle into his GT, and the rear upper link proved to be the biggest compromise, there's very little room. There'a thread showing pictures of this mod.
Yes, there's very little room. If you pick up a few books on performance handling you'll be able to see most of the approaches that people have used and then you can decide which will fit best for you. When I build my Manta which will also have a Toyota rear axle I'm planning to take a different route than with the GT. I'm thinking of using two upper links located in the wheel wells. There isn't much room side to side but lots of room vertically. This should allow for lots of adjustability in the brackets. On the bottom, I've not decided but am considering two links that converge at the center of the diff. This is a cross between a three link(no bind) and a four link(four links) and has the advantage of not needing a panhard bar...
However you do it, it WILL be a fair amount of work but it will be worth the effort if done right IMO. The availability of gears and LSDs is wonderfull....
Also, you'll need to keep in mind clearance for the exhaust. The toyota diff is relatively small compared to ford 9" and such but I still had to put a large notch in it to allow my 2-1/2" exhaust pipe to fit over it. Thankfully the part I needed to notch wasn't a casting...