The numbers don't match in the 1938 race:
http://www.kolumbus.fi/leif.snellman/gp386.htm#33
ERAs are #19 (Dobson), #15 (Connell), #18 (Cotton). Again the Maserati don't match.
If it was the '38 GP, surely there would be a Auto Union or Mercedes-Benz?
1937 GP doesn't match completely either.
However there are the JCC 200 miles races?
As I said before, I know nothing.