I came up empty, a D14 hood is 36 1/4, D15 is 39 3/4 and I didn't even go to the barn and check out the 17 since it's way longer. The D10/12 hoods are 30 inches but they aren't split. I took a look in the parts manual and the stationaries don't appear to use split hoods. I'm interested in what it is, in fact, it sounds like the type of oddity I like to put on the shop wall.
One thing I don't have here at the moment, is a Parts manual for the larger stationary engine based on the D17. Maybe that's it?
The photo shows D14, D15, and though obscured D10 and 12 in the background.