Well I can only describe for a 69 which I assume would be the same
What do I need to install the aftermarket floor console guages and the tic-toc tach on my 68?
you need the consol, the gauges and pod they fit in and the wiring loom to hook into the main loom...note there is also wiring to go thru to the engine bay for the ampmeter.
The unit we got for a friends resto also came with a wiring circuit
Do I need a new dash instrument circuit board for the tach?
No, that tach wires into the loom.
Also, how difficult is this undertaking?
Depends if you take the seats out or not..no seats lot easier
Seriously thu it is not diffcuilt , but is time consuming....just following the circuit diagrams, Wires are all colour coded...you may find a couple of wires that connect into the looms, baynet fittings inside the loom...not a problem you can feel them iside and a small cut.
If you have Air Con, pull the lower ducting out..a few screws.. to hook up the oil line and run the loom correctly behind and under it
We didnt have the radio in..pull that out to..makes thing comfortable.
Most important...get a small matress and pillow to make yourself comfortable laying on the floor...If you are comfortable, you think clearer and the job goes far better..and less stress hassles.
2x and 3x check each connection is correct before moving onto the next.