I'm a wheelbuilder. You mentioned the hop was opposite the valve hole. This is an assembly point for most rim manufacturers. The rim in question has a pinned joint, not welded and machined like currently produced rims. Pinned joints are prone to giving a hop because the aluminum was bent into a circle. The ends don't want to stay exactly where they were bent, so you get a little hop. Often, when building with older Mavic rims, a very calculated smack with a rubber mallet was what it took to take care of this.
IMO, spoke length in this case is irrelevant.