[Furback]

Actually, 492 straight plug heads were used in late production 1970, part number 3987376, this was also the superceded part number for the discontinued "186" 1969 Z28 head. Early production 70 Z28,s/Corvettes had "186" heads before the "492" was used. The Z28 and Corvette LT1 had 2.02X1.60 valve size and screw in studs. The "492" head was also used in 350/300hp but was a 1.94X1.50 with pressed studs.
71,72 and 73 used "487" casting, it was a large chamber 2.02X1.60 on the Z28 and Corvette LT1. Low horse passenger cars also used this casting but as a 1.94X1.50 and pressed studs. A friend has some M dated 1.94 492 heads, he got them off a 300 HP Taxi.