Here goes. My 90 did not have a radio when bought. The stock amp is
still there.
I bought a Kenwood KDC-222 radio to fit the opening. In addition to this,
I am buying a 99-5025 dash kit and a 70-1770 HRN.
The radio did not come with the mounting sleeve so I am getting one.
Question, what else do I need to make this fit? Also, I have been told
on prior posts that the stock amp is not too good. Is there an alternate
that may fit in the same spot that is better. Or should I just eliminate
the amp and just use the radio.

 

follow the hrns's that go to the amp and one will go back behind the glove box and connect to a matching wire hrns. If you disconnect that hrns you will see that it matches the 1770's speaker hrns that you bought. You can gently pull that hrns back to the radio opening and then you have bypassed your amp and there is no reason not to pull it out of the dash.