The original type bolts to the head and is a partial filtration system. Ford used the partial filtration system until the end of flathead production in both standard installations and optional installations on the older V8s. Only a portion of pressure oil was filtered in these systems, not all, since only a portion of pressure was diverted to the filter housing.
Many modernistic builders and hot rodders opt for a full flow system which can use any externally mounted filter including spin-on types with custom brackets but this requires modification to the engine block and/or oil pump to accomplish. Some run the pump pressure out the side of the oil pan to a filter than back into the oil galley at the back of the block. This would be the best type of filtration system but it's obviously not original for the purist folks.
Kerby