Detroit's are known for starting easily after sitting for years and years. Be sure it has fuel and oil. Also take the valve covers off and work the fuel control tubes by hand to see if the injector racks are free. If any one of them is stuck you will be in trouble when it starts, as it will hold them all in the same position and the engine will steadily and quickly gain speed till it makes a loud noise followed by complete silence. When you do start it have a hand on the emergency air shut off in case it tries to run away.
Parts are extremely easy to get, piston and liner kits run about $100 a hole.
The 53 series came out in 1958
6V53's are quite common, the 8V53 is a little harder to find, but I would not say they were rare. The hardest to find is a 12V53, essentially two 6V53s bolted together. I have heard differing reports at to how many were made, from 300 to 20, but not many.
Any more Detroit questions?
Grigg
