The studs are simple screw-in items, but several decades of being threaded into the manifold might make them a little hard to remove. I'd suggest threading two 3/8-24 nuts onto the stud, and jamming them tight together, then using the lower nut to try to back the stud out of the manifold. If it's stubborn, apply penetrating oil, and heat if necessary. Vise grips or a small pipe wrench are a last-resort method. Just don't twist one off trying to get it out. The stud will have a 3/8-16 thread into the manifold, and 3/8-24 threads at the carburetor flange. They're standard hardware items, but you might need to find an industrial supplier like Grainger or MSC, etc. to find a good assortment of lengths to fit your needs.
Jerry
