The HD originally has the parking brake on the rear of the transmission because the HD trucks have 4 wheel disc brakes. I actually own one of these trucks, but have never taken all the parking brake parts off to see what's under it. I'm still moving stuff from my old house to the new one and using this truck with electric gate, and box body to move, so I can't answer that question.
I've never seen anything in print that you can't use the HD transmission, maybe a call/E mail to Jake's would give you the answer about what parts are different , if any on the HD transmissions.
I did a quick search and found this about output shafts:
https://ls1tech.com/forums/automatic...-variants.html
I also found this, and it says that the HD version is actually a beter candidate because some of the better parts in the transmissions:
https://ls1tech.com/forums/automatic...-4x4-swap.html
I guess I'll be looking for the HD/motorhome versions from here on out....
