If my memory is correct, you are correct that all 383 blocks were not drilled and tapped for the A body mount just like all 440 blocks, although different than the 383 were not drilled and tapped for A body mounts
Those tapped holes could be used for other accessories such as power steering? Anybody could have drilled and tapped those holes. I have a '69 440 block that has the tapped holes above the oil filter which is where a 440 A-body motor mount is mounted......that doesn't mean it's a factory 440 A-body motor..........
There is one distinct fact that all factory 383 A-body blocks had machined off the block from the factory which the pics show is not.
