MetroMPG -- You're right, putting 'boat-tails' in the title helped. That shape silhouetted in the last picture would have in inverted T-shape to the truncation. I have 3D model of that; I will clean it up and post it.
As far as fabrication skills go, wood>metal>fiberglass. Cost of materials is another consideration. I have a good supply of redwood benderboard, 1/4"x4"x12'. If it was vacuum-bagged it could produce something like this:
Howard Hughes airframe crew produced those during downtime while they were building the H-4 Hercules. Wouldn't one of those be a barn find?
What I'm leaning toward right now, is to replace the rear lid with this plastic cargo pod. Here it is mocked up on the '58 baja:
and it would be easy to hang K-back on the bike rack:
My focus right now is calibration and instrumentation. (I did replace the outside mirror). I found a city radar trailer (You are going xx mph) and drove into it at 3 speeds spread across 15 mph. It only reported 4 mph difference, so that didn't help. Next week, after a train trip to Seattle, I'm going to take a road trip and burn a tank of gas just to get a base-line for comparison.
botsapper -- I've got one of those, too! That's more work than I would ever tackle, the only part you could reuse would be the chassis and nose. You can totally get a Type II that low, but I'm skeptical about the rear door hinge line.