I think a lot of people would agree that you may as well ask how long is a piece of string? Sorry, but all of these tasks could take a couple of hours to a couple of days. I fitted a stereo to my cruiser the other day, bolted the head unit under the dash, ran the speaker cables,  bolted the speakers to the rear shelve (factory 6x9 holes!), wired up the head unit and away I went. All up about 3 hours work, then again it took two 14 hour days to do my wife's Nissan Patrol, complicated car with a big system. All of the changes depend on what you are using, what motor, what air-con etc,etc. All I can suggest is gather your cash, get quotes and seek advice on the best people to do the job. The cheapest quotes aren't usually the best places to go to either, read magazines, ask questions, surf the net, you could well do some of the work yourself to save money.
Have Fun!

I found in general the following usually applies $0    - $3000 : Poor to Average Condition, parts and trim missing and usually a fair amount of rust. $3000 - $6000 : Average to Good condition, some may have rust spots, generally the cars are complete and usually modified $6000 and up  : Good to Excellent condition, concours/show winners. To get a perspective on the current pricing go to http://www.tradingpost.com.au, search for "fc holden" and select "all publications". You will get a listing of FCs for sale all over Australia.
Good Luck Keep in mind these cars are over 40 years old now so a completely original car would be hard to find.