289HD, aka GT40 heads-
There's an "early' and "late' design with regard to the spring pockets. (Early as in like the 289HP spring pockets, late as in machined in look/change in the head casting).
They used the close tolerance pushrods slots like the 289HP. The combustion chamber CC numbers are larger than the 289HP. The intake port is superior and the exhaust port
is far superior as compared to the 289HP. The only exhaust port close to that of a 289 HD would be those on the 302TP. They use GT40 valves, which are larger diameter than 289HP. (i.e.: 1.875 and 1.625....... pretty sure some were raced with 2.02's also)
Your brain-trust on these things would be Craig Conley, Randy Gillis, Jay Cushman and I'm sure a few others on this forum.