Actually, the Russian researchers that first reported the detection of element 104 (later named Rutherfordium) used a different reaction; they bombarded a plutonium-242 target with neon-22 ions and separated the reaction products by gradient thermochromatography after conversion to chlorides by interaction with
(242/94)Pu + (22/10)Ne -> ((264-x)/104)Rf -> ((264-x)/104)
The reaction your equation describes was set up in 1969 at the University of California, Berkley; scientists here bombarded a californium-249 target with carbon-12 ions and measured the alpha decay of
(249/98)Cf + (12/6)C -> (257/104) Rf + 4n
So, to answer your question, four neutrons were generated in this reaction.
More on Rutherfordium here: