Question about a trans I have.

I have a 1978 727 that is for 400/440 . It is a HD, long tail shaft housing & rear timing hole.
I counted the teeth on the input shaft, there's 24 so it's not a lock up trans.
I also have a standard 440 trans from 1975.
So for ***** and giggles it's for my 70 dart, 470 stroker. I've been talked into going with a transbrake (cope) rvmb clean neutral after 3rd gear and turbo action shifter.
Is anyone familiar with the later hd transmission?
Is there anything in it that really justify it being an HD as in usable for my drag car ? Dyno time coming early October but a guess is 640.
Edit; not planning to use it stock