The rubber boot is repo'd by the Buick Farm. They may have it listed on eBay too.
The spring- Sean at paintworks had some extras made up.
Flywheel cover- One from a Dynaflow will fit with a few mods. I did a how-to, it's somewhere on this site...
The lower adjustable linkage- you can make one using a yoke from McMaster/Grainger and some threaded rod.
Do you have the lower frame bracket? It bolts on. At least you got the upper mount, that's the hard one to find. The lower can be fabbed, I had to make one.