It could have been a 3 i will check out tomorrow. The 3973370 heads are the only ones i could find also. These heads have been ported and polished and he wanted to trade some parts so i was trying to see if they were something special or just like other heads. Thanks and if anyone knows of heads with these #s please let me know. again the # looked like 3979370 could have been the light or maybe i just don,t see good anymore must have been poor light