Advice on Motors for WED Tredwell 327-T Droid

I am looking to make a tracked vehicle that is very similar to the WED Tredwell Droid from that popular space fantasy movie (see link)

starwars.wikia.com/wiki/File:327-T_droid.jpg

My biggest concern is weight and motor size. I have an existing Sabertooth high amp controller from another project that I am going to use for the drive controls. I expect to to be using 12VDC batteries. What I need help with is motor selection. What would be a good motor for the weight of the robot I expect him to weigh in between 45 and 60 lbs. I will be using a wooden box in a box frame with lexan or ABS panels. The core shaft will be PVC.

Any thoughts you have would be great

Here is my parts list for the track design please make any corrections you feel necessary.

Track - 3" Wide x 21 links ~23" (single) X2
SKU: TRK-02 $77.90


Passive Idler Hub - 3" (pair) X3 (three pairs)
SKU: HUB-13 $44.85


Track Sprocket - 9 Link (Pair) x10 (two pairs mounted back to back in the front, 3 singles per side)
SKU: SPRK-02 $19.90


Universal Hub - 6mm (pair) (adjust per motor please)
SKU: HUB-02 $8.00


Aluminum Hex Standoffs (F/F) - 1-1/2" x 1/4" (4-40 Tapped) (10) X2 (approx 8 per side)
SKU: AHS-04 $13.90


Nylon Bushings for Track (10) (approx 4 per side)
SKU: NB-01 $9.90

Simple ASCII drawing of my thoughts on the layout
S=Sproket
B=Bushing
I=Idler

                     ___________________________
                 SS|motor                          motor|SS
                   B|                                         |B
                 SI |                                         |IS
                   B|                                         |B
                 SI |                                         |IS
                   B|                                         |B
                 SI |                                         |IS
                     ___________________________