61-71 D100 or D200 would probably be easier to find and you have to narrow it anyway. Nostalgia Sid's probably can fix you up with drop/raise and width. I have one in my 64 D100 with disk brakes.
I am considering the Speedway Motors route. The 48" wide works out about right, straight, 4" drop, 6" drop. Couple different brake options also. I'm thinkin the 4" drop. I think with the straight axle, a beer on the dash will spill in my lap due to the nose high attitude. That would be with the Dart at rest and not on the public hiways. Save the Beer!!