Sal is a whiz at rebuilding Holley 4000s and like me, I believe he gets most of his parts from Daytona Parts at
https://daytonaparts.comI have purchased the bushings kit from TeeBird AutoParts in Exton, PA. Their website is
https://www.tee-bird.com, but you are better off just giving them a call during a weekday. Bill Stratton and the boys know their stuff, but their website is a little wonky.
I do have some rebuilding information on my personal website and there are some handy videos if you are interested. The main like to these blog posts are here:
https://www.hotrodreverend.com/blog/categories/carburetor. If you scroll down on that page, there are quite a few blog entries where Holley 4000s are highlighted.
Daniel JessupLancaster, California
aka "The Hot Rod Reverend" 
check out the 1955 Ford Fairlane build at www.hotrodreverend.com