72 dart backspacing question

Option 1 and 3 will not be the same unless you get custom axles to reuse the small brakes and reuse/drill the drums. Otherwise most off the shelf LBP conversion axles use the wider lbp drums. I needed a 17x8 with 5.375" offset to fit 245-45-17 under my 69, your 72 will have a more room in the front and rear than the 67-69 Darts. Now if you go LBP front conversion as well this adds to the offset too. I went with a 17x7 x 4.75 as well.

This is a good read

http://www.forabodiesonly.com/mopar/showthread.php?t=225071

To sum it up, if you change to LBP, you'll need a more posative offset (i.e. more back spacing) wheel, front and rear depending on what you decide to do.