It is a little time consuming. Figure two to four hours the first
time. You need to remove the radio and SID, remove a couple panels
under the dash, then 10 (AFAIR) screws holding the dash in place. easy
from there. I recommend getting a Haynes manual to help locate the 10
screws.

A couple hints:
- disconnect the battery or I can almost guarantee a trip to a dealer
to have a Tech II unit reset the SRS light

- Use small wire ties and wire the little grills in the heating vents
together with the cross bars so they don't come apart (the cross bars
are a "+" shape that crosses at the center of the control knob in each
vent).

- Put the old SID unit back in.

- I forget if the radio code situation switched in '99, but you may
need to have the code handy to reset the radio if you disconnect the
battery. If you don't have it, the dealer can look it up if you have
the VIN.