Westach made the dual a/f gauge. The gauge housing was a little smaller than the clock housing. I cut the back of the clock housing off and slid the Westach gauge in. They can make pretty much any combination you want. I used Innovate LC-1 senders. You can recalibrate the LC-1 via laptop to work with any gauge.
In my gauge combination the oil pressure, oil temp., and fuel gauge are stock Porsche gauges so I used the stock senders. The tach is by Stewart Warner. I took the tach apart and had a new dial overlay made to match the Porsche lettering. I took the tach signal off the coil.
I took the fuel sender out of the gas tank and measured the values at full (.003), 3/4 (.020), 1/2 (.035), 1/4 (.051), empty (.070).
Steward Warner makes various fuel gauges available with different values.