If its a numbers matching 340 4 speed car fully restored id say its worth around 50k. not very many demons produced as it is and a original 340 4 speed with original engine trans and rear is getting pretty damn hard to find.
If its as clean as you say it is, and has matching engine trans and rear id say easily 10-13k
If i were to buy it, and if it was all numbers matching id put it back to factory, at the most id put some radials on it, you could always have 2 sets of wheels for it, one set with radials to drive it and one set with the old biased tires to show or even to sell it