There are sveeral model companies that have made '73 Challenger models, or should I say '72-'74 Challenger models.
The first one posted by 72rtchallenger is branded by Lindberg/Testors. It does not really have good proportions. It's more of a modified version rather than a stock version. The Testors kit I have comes with a Superbird style nose cone to put on, maybe Lindberg as well. Have fun with that! A Super Challenger!
The second one by 72rtchallenger is made by ARII, a Japanese manufacturer that used to be under the name Otaki. I have a few of thier kits. Depending on the age of the kit, there are some variances. If you look at my signature, pic #2 and 3 are of a later model ARII kit. Despite being labeled as 1/24 scale, thier cars are actually a little bigger/wider than the standard 1/24 scale Challenger, let's say a '70 made by Revell.
The advantage to this kit is that it has opening doors and hood, raised "Challenger" script on the rear quarters that's easy to paint and is steerable. Big disadvantage comes when you look at the interior and engine. That can be remedied with some kit bashing with another Mopar kit. The rims that come with the kit are a set of Magnum 500s that don't look that good IMO and a set of chrome slotted rims. Also the suspension isn't that detailed as these cars were designed to be motorized, so that means a flat pan chassis with detail molded into the pan.
Older Otaki kits will have slotted rims that look like brushed aluminum, have a motor, rear axle with plastic gear, and associated electricals to get the car moving. Would make a nice candidate for a radio controlled car. It's kind of variable what wheels come in the kit and if there is a motor or not.
There are some older kits made by an American company back in the 70's, I think MPC or Revell, but those kits are hard to come by and are very expensive. The ARII kit might be found locally at hobby stores for like $30 or on Ebay. I got an older ARII kit with a metal gear box for like $12 on Ebay a while back ago. Lindberg/Testors kit from the linky 72rtchallenger posted or Ebay.
More pics of my model can be seen here is interested. It has different tires and wheels than the ones in the kit.
http://www.cardomain.com/ride/456046/3