While I agree with the good advise given here, let me tell you what happened to me about 45 years ago.
I had a 63 Windsor, with a tired 383. A friend had it out and he called to tell me the timing chain had jumped. He said a "mechanic" had checked it out. We towed the car home and when I was changing the very loose chain, I realized it had not jumped. In the end I learned that the engine had been flooded and the cylinder walls washed down. Solution was to remove the plugs, squirt some engine oil in each cylinder, spin the engine and install the plugs. The engine then started and, after the oil smoke cleared, it ran well.
Just in case it might be useful. Lindsay