12V isn't that hard to do, only part you really need is a 12V wiper motor and coil, swop all bulbs and separate the dash feed with a step down 12-6V brick, that way fuel/temp/oil pressure senders stay as is, lightweight alternator, I'm still using 6V starter, just spins quick like a modern car, it's been on three years like that.
Little Cheekycunto battery, dump reg, add modern flasher unit etc, you can add a stereo, fag lighter, charge phone, sat nav, cheaper more available battery.....takes the faff out of having 6V.
6V is fine if you're after originality, works perfectly well in good nick, but can't see the point of keeping it otherwise, cos it'll always be a stumbling block if you're gonna 'use' the car.