I did the 8 volt battery deal 30 years ago. Adjusted the voltage regulator up and didn't burn out any bulbs. I ran it until the 8 volt battery died of old age. I couldn't find another 8 volt battery for a decent price, so I went with a 12 volt conversion with an alternator.
The thing I liked about the 8 and the 12 volt battery was how it made the 6 volt starter turn the engine over so much faster which aided in dependable starting under less than desirable conditions. (Another topic worthy of further discussion since these "less than desirable conditions" are often the reason why some of us went with 8 volts to begin with.)
I am guessing that the reason why I did not burn out any bulbs was due to the natural loss of voltage inherent to these trucks (like the one which requires relays to make the headlights to be bright with 6 volt systems).
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission