Nineteen-thirty six is when the new six cylinder engine came out and the term "Stovebolt Six" was coined. The '37-38 GMC's used the Olds flathead six in lieu of the Chevy six.
As far as I know the term "stovebolt" has always been associated with the Chevrolet 6-cylinder engines that were first introduced in 1929. I've never seen a GMC engine refered to as a "stovebolt" engine.
I'm also not aware of any 1930's GMC trucks being built in the US having factory installed Chevrolet engines...
The light duty 1935/36 GMC trucks had the Oldsmobile 213 L-head and the 1937/38 used the Oldsmobile 230 L-head.
1939 was the first year for the all new 228/248 light duty engine designed by GMC...
Mike B
