electrical issues with the 67 fish

Sounds like you have a starter relay for an automatic, exchange it for one for a manual. I agree with Redfish , it sounds like there`s no ground. You may have also pulled something loose when removing the instrument cluster, make sure your plugs to the back of the ignition switch and circuit boards are all still fully making contact. There are two positions when you turn the key to the right on your ignition switch, an "ON" position the first and a "START" position the second. Check to see you have 12 volts to the on postion wire (been a while but I think it`s the red wire?) and then see if it checks for 12 volts again in the start position (dark blue wire?) when you turn the the key to actually start the car. If it worked fine before removing the instrument panel then chances are it`s a ground or you`ve pulled something loose. One other place to check is at the bulkhead connector in the firewall, a lot of room for something to get loose there.