The Parking brake drum was used by Chrysler in the early 60's ( 60-63)just before the "P" was developed where they locked the transmission internally for parking.
. I have that early arrangement and I wished I had gone to the next generation 727. The simple reason is that the drum brake will require adjustment while in service. You also have to fabricate the floor with a hump for that drum.
There are plus's and negatives. AT least the drum brake gives the operator a foot brake and an Emergency brake option.
With the 727 fitted to an early machine one would have to fabricate a braking system which I don't think would be hard.