Looks as if he did a nice job in updating the 73. As lear4406 stated the 440 was offered in the 71 Challenger as well as the entire range of performance (and non-performance) engines The 8 3/4 rear is all you need for the street, and works behind the 440, even if you were to "build" the engine. The Dana rear was top of the line for heavy-duty high-performance use..but is over kill for street machines, and very $$$$ today.
The 73 was available with only two engines, the 318 and the 360 small blocks.
One question...does the Challenger have the Rallye dash? (Four large gauges surounded by wood grain panel)...not really needed but just prefered by many.
If it's priced well, it would be a good buy....it all depends on the price....
(Looks a lot like one that for sale in Scottsdale at the Russo and Steele car auction last January)