You're welcome! If anyone needs either the 240z or 280z white face for all your gauges in MPH, just PM me with which set you need, and an email to send it too.
I would go with the flange tool. Are you going to replace the whole quarter panel, or splice in part of one? You can use the tool to punch holes along the edge for the whole panel, or flange to splice one on.
Most napa, and car quest auto parts stores can make up or order you a custom made cable.
Also:
http://www.speedometer.org
http://www.speedometersolutions.com/speedometer_cable.htm
http://www.speedometerplus.com/quote_new.htm
These are just some I found.
I just bought one of these:
http://cgi.ebay.com/ebaymotors/14-LED-Car-Rear-Brake-Stop-12V-Warning-Light-Lamp-Red_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14QQhashZitem3a50f74bb2QQitemZ250466487218QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
They come in different lengths, and just stick to the back window with extremely sticky tape. They are shipped from Hong Kong. I got mine in about 5 days.
Do you have a Duraspark distributor? That article says you need one.
The voltage dropping while cranking is normal.
Does the engine block have a good ground to the frame or battery?
It looks like something is missing. I would either add louvers, or maybe cover part of the window with sheet metel to make the window the same shape and size of an early Z.