Here's your enclosure imported into AD6.8.
I took the following steps:
1. Import DXF into AD6.8 PCB editor using defaults.
2. Look at PCB List Panel and find that the primitives are at coordinates (130in,176in) which are outside the 100inx100in workspace.
3. Open a clean PCB in the editor, import the DXF using inch Acad units and (-100000mils, -100000mils) as the Acad (0,0) coordinates. This placed the imported primitives in the allowed AD workspace.
4. Select all and move selected to 2000,2000. Reset the relative origin to place the enclosure reference at 0,0.