[joyridin']

Since nobody with more knowledge than me has answered, i will give it a shot.

As far as i know, all Butler Cobras had a number on the left front frame rail that started with BR. Arntz Cobras did not have this and it is hard to tell one from another as far as what year or when it was built.

The easiest thing to do is take pictures. The engine compartment is a dead giveaway for a Butler or Arntz, but the interior, pedals, and maybe even the front suspension would also help.