99-01 tails on an 03-04 cobra
03/04 harness has 3 brake light bulbs, and 1 reverse bulb. The 99/01 have 3 brake light bulbs, 1 reverse, and 2 for turn signals. So you can't swap the harnesses between the tails.
But the housing with the correct harness should work fairly easily. Just have to swap both parts over, that is unless you want to do some splicing.
Bullitts are better than Bullets