Hi Jack,
I was all set to swap the jeep to 12v but was stopped by Tony Sudds advice.
His words of wisdom were, if it needed to be 12v uncle sam would have built em 12v.
Its often other areas that need looking at , battery leads need to be heavier for 6v to prevent volt drop, connections/earths need to be good, compressions need to be OK.
I looked at my valves and redid them, hey presto better starting and still 6v.
There is no saying its your valves Jack but there are other areas to check before jumping to 12v.
I'm not a rivet spotter so I have no problem with swapping to 12 volt for practicality but seems a shame to change it for no reason.