This might be better asked on a T-Bird forum... or at least research on T-Bird forum.
The only difference between the T-Bird and LS, (that I recall), is somthing to do with the front shocks on the early T-Birds. But I'm also thinking, (vague recollection), that the T-Bird used a few more Jag parts than the LS.
First, (and best), option...
Might be best to call a dealer and see if both vehicles have the same part number for the rack... for your year LS. This would also allow you to get the current factory part number to use as a cross reference.
2nd option...
The T-Bird rack MIGHT be the same... but IF you want to be sure... take some pics of the rack on your LS... to compare with the used T-Bird rack.
Also... take some measurements:
- overall length of rack housing
- diameter of rack housing
- total length with tie rods
- spacing of mounting bolt holes.. both on the rack and the sub frame
- location and length of housing extension where the steering shaft connects, and diameter of steering shaft connection
- location and size and type of fittings for the hoses, The hosr connections could be different
- any other visible differences
The outer tie rod ball stud sizes and/or rod sizes may be different... depending on the year. This could be more the issue... because if they are a different size, it could mean having to swap knuckles... and those on the T-Bird might be different too... especially with the LS using 2 different ball joint sizes for the knuckles, (based on GEN).