Wheels sitting out of centre in rear arches

[J1MMY]

I'm currently in the middle of swapping out the SM420 for an NV3500 so have been spending quite some time admiring the underside of the truck, contemplating a few things.

I'd like to cure the issue of the rear wheels sitting forward in the arches and can't see why the trailing arm crossmember can't be re-fixed the appropriate distance rearward? I am already having to do something with the park Brie assembly as the crossmember for the trans sits over the park brake crossmember.

I'd be interested to know if/what others have done to centre their rear wheels.

EDIT - found this.... http://67-72chevytrucks.com/vboard/s...d.php?t=666315

I intend to do something about the shock mounts anyways when I swap axles but the spring perches require more thought.