I'm a bit late to the conversation, but I've not seen a plug at that location on a 235 before. It is not a typical freeze plug location (as Jon pointed out). Here's a '53 passenger service, full-pressure 235 that I recently picked up (engine serial number prefix LAQ). There are two freeze plugs on that side of the block, but the "standard" one farthest to the rear is over the throttle linkage stud, well forward of the plug on that block, and similar to images others have posted.
