I have a 1966 Westfalia which is currently undergoing a transmission rebuild and an engine replacement.
The engine that I have to install is a 12 volt engine from a 1971 Karmann Ghia. 
I think that this might be an appropriate time to convert  from the standard 6 volt system to a 12 volt system.  
What unexpected problems have others encountered doing this and is this a worthwhile change?  
As far as I know I'll have to:
change all the bulbs; 
get a 12 volt voltage regulator; 
a 12 volt starter; a "6 to 12 volt" starter bushing; 
a 12 volt battery; 
and a voltage drop for the 6 volt wiper motor.

I'm also concerned that I'll need to change throwout bearing forks to accommodate the newer clutch assembly.
Is that true?
How much and where do I need to grind the bellhousing to accommodate the larger flywheel?
Any help you guys can provide will be appreciated. 
Camping season is here and I'm anxious to get back on the road.

My 66 single cab was already converted to 12 volt when I got it, but I think they used a wiper assembly out of a 67. 
This may be cheaper than a voltage drop? 
Also, don't forget the make sure the solenoid and choke are 12 volt on the carb. 
I've heard some say you can stay with the 6 volt starter and flywheel without any problems. 
Might be worth looking into.