Here is the transmission from my 327F, which I am NOT sure will fit your H motor, and I believe it will NOT fit your H.
http://www.network54.com/Forum/424840/message/1177901052
Here is a photo of my H motor in a 1956 Chris Craft speedboat I also own, and you can see there is a big difference between the 283H and the 327F or 283F. It does, however, look amazingly similar to the transmissions Chris Craft used on their flathead Hercules motors (see below) but those have a different bolt pattern to fit onto the V*.
Of interest, I am showing a Model K Hercules motor here, and note how similar the transmission is to the one on the V8 283 motor. The V8 motor has an aluminum transmission case. I believe the flathead Hercules is iron, although I don’t recall ever seeing what is under the blue paint. The bolt pattern is different from the Hercules 6 to the Chevrolet V8.
I can tell you, that the Hercules and the V8 283 were set up to fit onto the same engine stringers, at almost the exact same bolt pattern, and the transmission on the H motor will fit EXACTLY where the Hercules one was. Been there, done that, it fits!
Good luck! Let me know if you need any detail photos of my 283H (which is now actually a 327H)
Regards,
Paul