[Shift'n Gears]

I'm trying to find an original Shaker drain hose for my 78 W72, but haven't had much luck. So I am trying to find an exact replacement. While the molded drain hose for the 403's is re-popped, no one seems to have the straight hose. What makes it more complicated than going down to the local hardware store is that the hose has a crosshatched ribbed pattern to it.
I've got a low mile 79 TA with an original shaker drain hose that has this cross-hatch ribbing to it and over the past 20 years, when I have come across known original hoses, they have the same ribbed pattern to it. In John Witzke's W72 article you can see the same pattern in the hose as well under the red shaker, so I am certain that the ribbing is correct. I am assuming that GM used some sort of generic heater hose at the time. Does anyone know of any hose that has this same pattern to it? Also does anyone know the correct ID of the drain hose? When I measured the hose on my 79 (end of the hose not on the nipple) it seems like it is 15/32 (slightly smaller than 1/2 in but slightly bigger than 7/16.) but that seems like an odd size to me and was wondering if the rubber shrunk a little over the past 40+ years.