Got mine on Ehay for something like $150 a couple of years ago. '69's or '70's 351W heads are a good core for porting and will be a nice addition to the 289 so long as you keep the compression up with the larger 60-61 cc chambers. You can also deck them .020 to .025 to get the chambers down to 55-56 cc. Gotta mill the intake also.
i might have some if you would like them, im not gonna use them b/c i got aftermarket. they need to be rebuilt though... if you would be interested PM and ill look at them and figure out a price+shipping.