They are about 61-64cc. I had them on an 89 Mustang and I was getting about 240RWHP vs the stock 190RWHP. They will outflow your heads but will probably drop your compression pretty low. Is your 65 the A code or C code engine?
Those would drop you to around 8.2 compression. I wouldn't do it without replacing the pistons at the same time so you could use them to adjust your compression ratio back up. For instance KB116 pistons would get you up to about 8.9:1 There's a pretty good chance the valves would hit the stock pistons anyway, as stock c-code pistons didn't have valve reliefs (at least mine didn't) They just had a little bit of a dish cut out.