rear suspension help

[shortfleet67]

i have a 67 gmc sb fleetside..i'm looking into swapping out the dana as its about dead..i thought as i put another rear end under this truck i would do a flip to get it down some..i guess the more i look the more confused i get!!
it has a full set of leaves doesnt look like any have been removed..rear shackles look stock and untouched...when i look at the possibility of a flip no way is there enough room..as it sits if i flip it the rear end housing would sit right on the frame?..now i guess i could shackle the rear of the spring to get back some heigth...but as i look at others i dont see this...i assume this has already been lowered some how? i will post a few pics..right now there is 5" from rear end housing to frame..8" clearance from top of rear end housing in pumpkin erea to bottom of the bed..so what am i missing here? i'm not even sure a notch would give me enough clearance?

[shortfleet67]

more pics

[shortfleet67]

here is a pic of how the truck sits..i know it had to be lowered a little in the back just didnt seem like that much to me..front has stock spindles and 2" lowering springs 15" all the way around 275/60/15's in back