I am going through the same issue. Here is the only "original" '36 style I have come across, from BrassWorks, which has the recessed area in the top tank for the fan:
https://thebrassworks.net/collection...r-reproduction
My '36 has about 45,000 miles and the original radiator was repaired 25 years ago by a local shop (Northboro MA) whose repairman said if I ever needed a recore, Maine Radiator was a good source. The radiator is starting to weep again where the core is soldered to the top tank (same as before). So, I'd be interested in the experience others have had with cores from either Maine Radiator or Brassworks, or is a new radiator the best option.