From all the info I can find the word gasoline was changed to fuel in the 1950 model year on the smaller GMC trucks. I do not know about the larger series. That would make the gauge cluster for 1950 a 1 year only. The housings for the gauges in 47 2nd series are 1 year only also.

1947.2 GMC 1/2T SWB panel
1947.2 GMC 1/2T long bed
1948 GMC 1/2T short bed