Have just investigated the prime model of truck I am looking at modifying..
Looks like the radiator can be lowered, and the header tanks relocated very cheaply..meaning that hood in the mock up drawing will be VERY easy to fit..
We also have a later model Kenworth hood here we can modify easily..it has the modern fender lines, and would simply need sectioning to reduce width (New cabs much wider than old trucks), and the nose cone dropped to the new angle..meaning the time taken to develop this is significantly less (And associated costs!)
We would then simple have to remount the fan (Or a higher quality unit) onto the crank shaft..mount a modern aero bumper (slightly lower than original OEM) and then work on the rest of the aero..
Gives me the ROI estimate as shown in this spreadsheet
Please feel free to advise if you think my estimates are wrong...I am trying to be accurate and conservative..