The case has a journal (1) opposite a welded on boss (2) which is bored in alignment with the journal. [snip] but that doesn’t explain the purpose of journals and boss.
John
The purpose for the journal and boss is much simpler than you'd think. A long bolt with a spacer/sleeve went there. Besides the bolts that are parallel to the input shaft and secure the transaxle to the bellhousing, there are a pair of long bolts (7/16 UNF x 3 5/8 inches) splayed out at a 45-degree angle, which pass through the bosses, then through spacer sleeves and finally thread into the journal.
BTW those bosses are not welded on; they are cast with the bellhousing, and then machined flat. And that journal is not part of the gearbox! Or rather, it's not part of the gearbox case. Instead, it's part of the cast iron flange that goes on the side of the gearbox case, through which the stub axles pass.
Curiously, the GT40 parts book shows a locking nut along with this bolt, but I don't know what function that might have had, since the bolt threads into the side flange. And it doesn't show the sleeve?
I tried to find some good photos of a De Tomaso Mangusta setup, but none showed this arrangement clearly. The view is completely blocked from below by a chassis crossmember, and from above by all sorts of junk including the spare tire.
The early Panteras equipped with a Dash-1 ZF used the same arrangement, even though the gearbox was inverted. Here's a link to an excellent drawing of a Dash-1 ZF Pantera bellhousing and associated parts:
Pantera Store
The bosses for the bolt are very clearly visible; the bolt and spacers etc. are parts #18-21 in the drawing (clicking on the number hotlinks you to a photo of each part).
Among the innumerable differences between a Dash-1 and Dash-2 ZF are the sideplates. The Dash-2 did away with this whole 45-degree splayed bolt arrangement, and the current production RBT gearbox follows suit. However, as many (MANY) Dash-1 gearboxes were scrapped (for no good reason) by Ford, most ZF specialists probably have some of these sideplates sitting around, and they will interchange with the later style. So if you really wanted to be authentic, you could get a genuine GT40 bellhousing, track down a set of ZF Dash-1 sideplates, and away you go.
Note that the current Safir bellhousing has the bosses cast in for the bolts, but the holes are not machined in them, so you would have to take care of that detail yourself....
None of this does a darn thing about explaining how the clutch linkage works though.
In your photo, the Girling clutch slave cylinder is mounted vertically, with the pushrod pointing at the ground. It bolts in using two bolts at (3), and the cast boss (4) supports the body of the slave cylinder. The pushrod extends down and pushes on (5), which translates that vertical motion into rotational motion. You can see that the other end of (5) is attached to a cross shaft with a pinch bolt arrangement. That shaft rides on bearings and runs the full width of the gearbox, and is located at the very front of it, on the outside of the oily bits with all the gears etc., right below where the input shaft extends from the front of the box.
Pushing down on the end of (5) causes that shaft to rotate; on the shaft is a clutch fork with two feet on it, which press against the throwout bearing, and etc. and so forth.
