The frame rails near where the front of the leaf spring attaches is a good place also or if you do put them under the axle as near the spring perch U-bolts. the frame is the best place. Before you get under it I always rock or push on the bumpers to make sure it wont fall off the jack stands. Hydraulic jacks alone can loose pressure and blocks crack. steel jack stand are best. Here is a photo of another Falcon I own on jack stands near rear axle, been up on them for 2 years now.
forgot to mention watch out for rear brake lines on rear axle not to pinch them.
another photo with out axle in the way.
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