X heads

I wouldn't worry whether they have X, O, J or nothing all 340/360 open chamber heads until the 308 casting in the late 80's have the same port and have the same flow potential. Take what you can find at a good price. If you really feel the need for a 2.02 intake valve it's easy enough to cut the seats for the bigger valve. Unless you are looking for power above 6000 rpm the 2.02 intakes do not buy you anything and can hurt the power down in the rpm's you would normally run on the street.