Pull the head and see what the cylinders look like. I've seen many that are probably never going to turn over again. The head gasket would be a cheap expense if the motor looks good, but it could save you a lot of time jacking around, you will know for sure if this is the motor you want to exercise your efforts towards.

1955 was a long time ago, lots of stuff could have happened to that motor over the last 61 years. I've seen rebuilt motors that didn't last a month....Gene