Before you jump into anything....
Whats the biggest boat YOU have sailed on your own and how much experience do you and your crew have?
Why do I ask?, because ive seen people jump into boats that size because of what they want in a boat (because of some "dream" they had) instead of what they can actually handle.
These boats end up never leaving the dock if there is so much as a cloud in the sky and become bird nests.
Also, I would familiarize yourself with what things cost on a 39 foot boat ie; sails,furling,engine overhaul,glass work,rigging etc...minor and major (things happen)
Call around to get an idea because any boat from the 70's will eventually need it.
My boat is a 76 and did very well on its survey when I bought it two years ago.I have put enough money in her in the last two years to buy another one and I still have more to go before its the way I want it.Worth every penny because of what I paid for the boat and sentimental reasoning but worth mentioning.
The c&c 39 was a well built safe boat thats quick and points well but who knows what may have happened in the last 30+ years.Get a good surveyor.
I wish you the best of luck on your search.
c&c 33 tall rig