318 block and I don't know

Just throwing this out there, but it sounds like the previous owner had been planning to build a 347 stroker. You use off the shelf pistons and mill the tops down a little, and then either mill the skirts to clear the counterweights on the crank or turn the counterweights down to miss the skirts of the pistons. Turning the counterweights down may also allow the rotating assembly to be internal balanced. If I live long enough to ever get the numbers matching 318 block back in my 71 Challenger conv, this is exactly the motor I will build.