I do not have a stovebolt intake to inspect, so the following are general statements:
Years ago, we used to restore and sell lots of multiple carb set-ups.
Many of the manifolds had open holes for the carburetor studs. Using all-thread here would NOT work, as it would be impossible to tighten the studs to the manifold.
As mentioned above, the better FLAPS will have a stud assortment. Generally, the studs will have threads on both ends, with a non-threaded section in the center. This non-threaded section makes it possible to tighten the studs to the manifold, and if an open hole, will prevent the stud from extending into the manifold plenum. Dorman Products is one manufacturer (there are others) that has an excellent selection of studs.
The studs come in a number of diameters and threads. GENERALLY, GM used a course thread into the manifold, with a fine thread for the retaining nuts. If one is changing studs, one could also change the fine thread to course (ie all-thread), but I have always believed that engineers have a reason for their actions, and have tried to duplicate their work.
As mentioned above, double nut the studs for the purposes of either removal or insertion.
Jon.
