The 310 ended production in 1980. The newest one I find in a cursory search is a 1979 . The seller is asking $120K.
I didn’t see a '56, but a 1955 Cessna 310 formerly owned by Jimmy Stewart, and apparently restored in 2004, has a price of $47,000.
I don’t know how much engines or overhauls cost, but I’m guessing around $30,000 each for a rebuilt engine or for an overhaul (you’d have to buy rebuildable cores, possibly for around $5,000 each). And you need two of them.