I probably posted it before, but just in case.
You can substitute the internals from the 914 combination gauge and speedometer for those of the 356 gauges, or you can swap the 356 gauge faces and bezels onto the 914 gauge cases. Easy Peasy.
The result are a pair of beautiful 356 looking gauges with the more modern 12 volt VDO internals of those from a 914.
The 356 tach face, bezel and glass can be fitted to the gauge/case of one from a 924, but it'll be off by a bit. I think that the 356 spins up to 6,000, the 924 to 7,000. In the lower rev ranges, where shifting matters, the difference won't be too noticeable.
I did up the gauges for the Pre-A in this way and they look stock/sweet, and function perfectly.
Luck,
TC