See my comments to your questions below :
>2. My bug has a short piece of copper braid hanging off the "dash" >paddle. I believe it should go from the 'dash' paddle to a screw on one >of the vertical posts that supports the triangular top plate, to ensure >good contact between the dash paddle and ground. Is that right? Is it >important, or can I ignore it? And will the braid from RG-174 mini->coax work OK?
If the braid is missing or damaged try using some desoldering braid, it should be about the same size. When you are looking at the bug from the paddle end, it should attach to the post in the left. This is needed as you obviously purchased a Deluxe Lightning Bug which uses a jeweled movement. The synthetic jewels are actually an insulator so you need this strap to ensure a good solid electrical connection between the lever and the mainframe.
>3. I have a loose helical spring, that I think is the "dot coil spring". I >believe that it goes between the "Lever stop screw" and the main >lever. It looks like I have to fabricate something that fits into the hole >drilled into the end of the "lever stop screw", and holds that end of >the spring (the small-diameter end) in place. The large diameter end >will simply rest on the main lever. The spring will be in compression, >so the missing part can be as simple as a piece of wire, glued (or >forced) into the "lever stop screw". Is that right?
Yes it sounds like the dot coil spring. That spring should attach to a pin that goes through the lever vertically at about the point where the lever contacts the left stop screw (this is part #12 on the diagram I reference below). The other end of the spring doesn't fit over the stop screw but instead the screw that is above that (part #23). (i.e the stop screw and return spring adjustments are separate).
I don't know of a specific hangout for Vibroplex users and collectors but there are a lot of Bug users in the Straight Key Century Club (in spite of the name) so that can often be a good place to ask questions.
BTW ... I just discovered that I have an intact "dot coil spring" from a
junked Lionel J-36 that will fit your Lightning Bug. It has the pin attached. If you are interested drop me an email at ve3wmb at rac.ca and I will send the part to you at no charge.
If you are missing any other parts let me know I might be able to help.
(i.e. do you have both screws that attach the braid ?)
Best of luck