The pylon on the inboard wing was perpendicular, i.e. hanging straight down (except on the unique pylon for the big podded radar: see http://tailhooktopics.blogspot.com/2012/11/ad-4n-aps-31-radar-pod.html). The pylons on the outboard wing panel were perpendicular to the wing instead; they were also not evenly spaced.
The view from the side showing the longitudinal spacing of the outboard pylons.
As shown here, the outboard wing pylons were not "swept" at the same angle as the leading edge, i.e. the most outboard one was closer to the wing leading edge than the most inboard.
The external center-line pylon was introduced with the AD-4B and carried forward to the AD-5/6/7:
Note the interface with the oil cooler outlet: the forward end of the pylon is much deeper because it sweeps up into the duct (don't be mislead by the shadow).
I'm told that the Trumpeter 1/32 center pylon does not angle upward from front to rear as it should.
Early ADs had much smaller and less capable AERO pylons on the outboard wing panel. See http://tailhooktopics.blogspot.com/2013/12/things-under-wings-aero-pylons.html
AD-1s through -4s had a smaller inboard wing pylon than the 5/6/7. The later, longer pylon introduced on the -5 was reportedly necessary to move certain stores farther forward for ground clearance. It also added provisions for the 30-inch lug spacing required for some stores. In addition, it may have been desirable to move the loaded center of gravity forward, particularly on the -5.
Here is a direct comparison of the World War II era 1,000 and 2,000 lb bombs on the earlier pylon (note that the 2,000-lb bomb had 30-in lugs and therefore had to be attached with an adapter).
As noted above, ADs before the -4B/5/6/7 did not have an external center pylon. The shackle was mounted within the fuselage along with provisions for an explosive-cartridge actuated "foot" that propelled the bomb downward away from the airplane when dive bombing so that it would not hit the propeller.
Illustration from Ed Barthelmes
U.S. Navy via Steve Ginter