That's been a bunch of years ago! I did some research about the ideal placement. A book "Doorslammers" had some good information & also one of the performance spring companies at the time (don't recall the name & haven't seen them in quite a few years) had good drawings/charts of the ideal placement of the shackle as well. I just figured it from there. You can see in the one picture right behind the shackle is a rusty line, this is the original placement of the rear hanger...so yes, they are moved forward a couple inches.
As far as bed floor crossmembers, ect. I need to advise you, I moved the one above the rear hanger to clear the opening through the floor for the fuel cell. Im sure it would have been moved back which may leave you in a problem if the crossmember is still in the stock location. You can just barely fit your finger between the hanger & the bed floor
As Zieg mentioned, the truck actually goes up quite a bit when this is done (my shackles are "lowering" shackles turned over so that raised it up a little more than the stock ones would, however part of the theory was "long & strong" shackles so that is what I used) until you do the axle flip.
12+ years later...my advice would be look into "sliders", something like this
https://www.speedwaymotors.com/Speed...ders,2151.html to end up in an ideal situation. Lorne