Can you place base struts on an Sport LS? If so has anyone done it and how does it ride? Do you also need to replace the springs or are they all the same across the LS ?

I would go with stock sports, not soft, not hard and handles great.

The shocks (base/sport/euro) are interchangeable across all years, but the shocks and sway bars are designed to work as a package, so if you change from base to sport shocks (or vice-versa), ideally you should also change to the appropriate sway bars.

The difference between sport and non-sport suspension is all in the shocks and sway bars; the springs are the same. IIRC, they changed the spring rates in the '03 redesign, but the springs on all 1st Gen LS V8s are the same, and the springs on all 2nd Gen LS V8s are the same.