NAPCOs with Automatic Transmissions?

[G&R's57GMC]

The NAPCO conversion could be installed on any truck with whatever was on the truck.

So yes you could have a NAPCO with 3 on the tree, with or without O.D. , 4 on the floor or with a Hydramatic .

BTW the Hydramatic does have Park, to engage it you would put it in Reverse and when you turned the key off the PARK plunger would engage .

Does this seem odd to you today ?

Well back in the day it was common practice to put a MANUAL trans in Reverse when you parked.
So it wasn't a far stretch for GM to have the driver put the Hydamatic in Reverse.

Generally Reverse was the lowest gear in a manual trans and it would have a harder time turning the engine against compression.

More then a few vehicles ran away on hills when the driver didn't also set the parking (emergency) brake.