If you can bargain the owner down with a realistic estimate of what it would take to revive the boat, and if you have the skills and the will to fix it right, and if you have nice current P-39 owners willing to advise for the sake of keeping the "class" alive, go for it. But it might not be worth the effort or money.
On the other hand, it is possible to refurbish a 35-year-old boat to "better than factory" in terms of strength and systems, never mind finish. I've done that, to some extent. But my boat wasn't as far gone below the waterline as this one seems to be, so I got to relieve my renovation kinks by actually sailing between sessions of fixing.