Centering rear wheels in opening.

If you move the front perches back, then you will also have to move the rear shackles back, and probably re-engineer the working angle. I assume you know that.
1.5 inches is a looong way to go.
I'm not into the Mopar scene that deep, but I have never seen what you are looking for,either. .......................Someone might suggest moving the axle back on the springs, but would destroy the way they work. It seems to work OK for up to .5 inch, ( the most I have heard of), but 1.5 is a loooong ways
And yes, I have seen custom hangers right here on FABO.
And I guess if you put the springs into the frame rails, the problem is solved. They do make kits for that.

And yes, I have also seen that video where the car loses it's entire rear end as the car continues to bounce over it. The video appears to be at a slower speed, maybe 35/40ish mph. But think how dangerous that would be at other speeds. Point is I'm no welder, so I wouldn't try it.
Happy HotRodding