[joyridin']

Olddog has a pretty good synopsis of the car. A few added things:

The frame is square, although it is probably one of the heaviest frames around.
The MG front end can easily be replaced with one from FAST. Not exactly cheap, but it will do wonders for the car in both handling and weight reduction.
Most Arntz Cobras had Chevy engines. That is probably one of the reasons for the value reduction.
Parts are pretty generic like all Cobras. I bought a hood from Mr. Bruce and it fit with a small amount of modifying. The car was splashed off an original Cobra, so it isn't massively different than most other Cobras.
The hoop is a bit of a value reducer and where the gas inlet is located.
The Type III cars probably bring the most. You can tell them by the drip rail on the fenders where the hood closes. The Type II and Type I do not have a drip rail.