Hey.
Walt, being as I would really prefer that these go into a Speedster than a real 356, you can have everything for $350, I'll cover the shipping for you.
The gas gauge and oil temp gauge in the combination gauge are both 12 volt units so they'll work great in a Speedster.
The speedo works off of the driver's side front spindle just as it does on the VW so that's a plug and play as well.
The tach would be best if it used an aftermarket VDO or other make tach for the internals as you can buy electric three wire tachs that red-line at 6,000 pretty easily. The 914 and other Porsche tachs red-line much higher and would need re-calibration to work with a 356 face.
Not a big problem, but an added expense where as a basic 6,000 rpm electronic is cheap and easy to convert over to the 356 face. Two small screws hold the face to the mechanicals.
Perhaps the best idea would be to buy everything, sell the original 356 tach face and bezel on eBay and use the money for a reproduction Speedster tach that's already set up and ready to go.
Hope that this helps out a little bit.