All the above is reasonable comment if you are making the wiring harness yourself as "Jayhawker" did on one of his videos.
If, however, you get a ready made wiring harness from a company such as YnZ that specializing in that sort of thing, the time spent on installing it is much less and, yes, you can do it in four hours or even less. (There is another company back here in the Northeast USA that does excellent work as well. I can't think of the name of that company off the top of my head. Maybe someone will post it.) These readymade harnesses, while excellent, are not cheap but well worth the buck given lack of hassle of making your own.
Those company manufactured harnesses come with cloth coverings as original and are labeled so there is no doubt as to where they go. Those people put out products that are amazing and professional in every way.
If you'e merely going to piece-meal the job and just replace the frayed portions of the existing harness, then some plastic covered wire from your local automotive parts store will probably serve. Your call.
As to going 12 volts, i, as the others above, don't see any reason for that unless the 12 volts are need for some other than original reason(s) or dictating application(s0. Going this route may trigger unanticipated problems that don't need to be invited in on an old 36. just my opinion, Again, your call but remember the satisfaction that one experiences from having his car as close to original as affordable and desirable. The key here in the VCCA club used to be preservation and restoration. Should still be.
Good luck with your decision.
Best,
Charlie
Note: After having driven 41s since 1953 and owning about seven, the only time a 12 volt system would have produced better cranking power, and thus desirable at the time, is when an engine has been recently overhauled, etc and is still tight. No other time that i can think of. The secret of being satisfied with a 6 volt system is a good battery, good charging system, and good cables and grounds.
