Tabbymom, your 1998 Legacy Outback is the wagon version, right? The top tether anchor part numbers for your car are different from what was posted above, and they also differ depending on your car's body style. I will post top tether anchor retrofit part numbers for both the 1998 Legacy wagon and also for the 1998 Legacy sedan just in case. There are also two different Subaru gray colors for 1995-1999 Legacy models, apparently, with different part numbers for each gray color, so I'll post all of those as well. Then hopefully you'll have all the retrofit part info. you need.
The LATCH manual indicates the 1995-1999 Legacy wagon models have three 8mm weld nuts located in the rear top ceiling trim for retrofitting up to 3 top tether anchors. The 1995-1999 Legacy wagons use Subaru top tether anchor retrofit part number 96031AC070 for dark gray, or 96031AC080 for red gray.
If you have a Legacy sedan instead of a wagon version, the 1995-1999 Legacy sedans have three 8mm weld nuts in the rear filler panel and can be retrofitted with Subaru top tether anchor part number 96031AC000MU for dark gray, or 96031AC000RA for red gray.