Throw out some more info regarding your intent.....are you set on keeping the original engine block? You probably can find a serviceable block that is not frozen that would be cheaper than machining out the pistons and/or sleeving the original block. Are you intent on keeping the engine all original or are you wanting to modernize it a bit? Fortunately, the old flathead six was used in quite a few applications (even forklifts) and parts are relatively cheap and available.

You might search for a MoPar owners site that specifically focuses on the older models...they would have a good contact list of who specializes in rebuilds and parts.