For some odd reason the Duralite regulator with the lowest nominal voltage has rating 5,1 V. 4,8 V rating is not available, at least from them.

In any case I would find it very strange if the ignitions could not take a variation of at least 0,5 - 1 Volt. Most of the sensitive electronic components inside the ignition most likely are rate for much more than 4,8 V.

Kato