5 volt or 6 volt dash regulator for my 67 fish car.

I decided to check my gauges while I have the instrument cluster on the bench and I found I'm getting no output from the built-in regulator on the 3-terminal fuel gauge used in the 67 Barracuda. Since I have several hundred 7805 and a few 7806 regulators in stock I decided to give it a try and it works well (on the bench). My question is should I be using a 5 volt regulator or 6 volt? Some of the other threads seem to imply I should be using the 6 volt regulator because the gauges are designed with that in mind.

I know I could buy a better regulator from RTE but it wouldn't be free.