Your floor (or perhaps inner wheel arch) is different from mine David.
I only have one bump stop, and that's hanging on by a thread... but its front edge (where it fixes to the floor) is perhaps an inch aft of the rear edge of the floor support bracket which mounts on the chassis extensions. Or 1/2" aft of the triangular fillet which I think your floor lacks. The centre seems aimed at the position of the axle beam on full sweep, and I suggest that's the main consideration here.
I don't know whose photo this was (apologies) but it shows them fairly clearly.
Here's another view:
I only have one bump stop, and that's hanging on by a thread... but its front edge (where it fixes to the floor) is perhaps an inch aft of the rear edge of the floor support bracket which mounts on the chassis extensions. Or 1/2" aft of the triangular fillet which I think your floor lacks. The centre seems aimed at the position of the axle beam on full sweep, and I suggest that's the main consideration here.
I don't know whose photo this was (apologies) but it shows them fairly clearly.
Here's another view: