The difference in a 48 head and a 52 head is that the glow plug is recessed in the 52 head. All the unthreaded portion of the glow plug is inside the combustion chamber. This gives you about 300 rpm.

The push rod tubes are the same on a 48 and a 52.

The 40 cam fits in the 48 and 52

The 52 carburetor will fit perfect on the 48 with no modifications. So will the Magnum/ASP 52/61 carburetor.