"The advantage for the E12 is that the motor doesn't have field
weakening, so it's about as simple as you can get."

Having done a few curtis conversions on e15/e20/I-5 i can say that it is very easy if you want to completely rewire the machine. I had plans that i sent out into public domain almost a decade ago. All you need to make sure of is that you have a controller with high pedal disable, and put a 3a fuse on the field.