If I understand your description of the seat binder issue correctly, it's not actually an issue. You can simply use a binder bolt that has Allen sockets on both sides. This requires the use of a pair of wrenches, of course, but how often are you changing saddle height?
Another solution is to simply grind off the entire mess and use a clamping collar. This is a poor thing to do to a nice bike, but most "mid eighties" Bianchis aren't that nice, and that's coming from a Bianchi collector. But to correctly, if you want to answer your question, have a framebuilder replace the the binder, you're looking at about $100 plus paint.
As to the cable guide, this is super simple braze-on, but again, you then require a repaint. A clip-on type cable guide is the simple solution.
Bottom line, AFAIC, is that unless this is a top-end bike and you are willing to blow about $800 on repairs and refinishing, you should keep it as simple as possible. HTH!
Last edited by Six jours; 06-27-08 at 09:52 PM.
Reason: Freinds don't let friends drink and post.