Welcome to a great place for advice on your build!
Big torsion bars & sub frame stiffening with good shocks will go a long way to getting you there.....from Boone.
Appears my trans bracket has been switched with a column shift car?...
Anyone got the longer trans bracket with the two studs? Mancini doesn't show one.
In 1973 the shaft size changed (Larger). Call Firm Feel (Left Coast) or Steer & Gear (East coast) They most likely can fix yours, My 73 Challenger has a power steering box from a 1980 Diplomat, Steer and Gear E-Mailed me the day they received it to let me know it wasn't original.
The torsion bars that came in your car are small. At a minimum you should be running the .92 dia.(440) bars
Go larger for more handling and less chance of oil pan damage.
Also consider some type of skid plate that could be attached to the K member.