I think the price is a bit high for used X heads. They are a decent lower end head similar to the Edelbrock E-Streets, which you can get assembled for $1,035 on Summit. I bought a pair of X heads that had never been run, with ARP head bolts & sleeve washers for $800 a year ago. The 64cc chambers will likely lose you a bit of compression, 58cc chambers are a better option.
'65 A-code coupe, T-10 4-speed, 8" 3.25 limited slip