What I recommend is keeping your 6 volt starter, if it is operable. I've been running mine on 12 volts for about 4 years with no problems. They say not to crank for over 15 secons at a time, but the starter is a tough one.
For the alternator a 10SI is the easiest swap, even works with the stock brackets with some modification. Get the 3 wire style. Also go the Fifth Ave Auto Parts (in the links under electrical). Randy sells a book on the conversion and the DA plug that make wiring simple.
