What can I replace the original headunit with?

The original head unit that is installed now is sounding pretty good when it works, but most of the time it doesn't. If there is a way to fix it - that would be great, don't know how. When I do a scan for stations it just keeps scanning and scanning and never stops at any station, if I do a manual tuning it does find the station I want (sometimes) and I can lock it in, it works for awhile and then disappears, :headshake i can only hear a white noise when tuning (switching) to that channel.
I have a pretty decent Kenwood unit (single deck) on my other car but have a hard time imagining how would it fit into that doubledeck rounded opening.
Any ideas?
Thanks!

You have to go to a stereo shop and ask for a mounting kit for your car the will fit the aftermarket head unit

Go to crutchfield.com They have the trim kits with or with out the little pocket under the unit.

Also, it is HIGHLY advised to get the adapter for the unit to the body harness. This will make your life ALOT easier. When splicing, remove the positive battery cable so that you dont get any shorts. Alot of people ruin their cars because they do not do this.

Thanks a lot!
I've read on some post about getting adapter - just wasn't clear of what they meant, now I am.
I've also considering going to the local stereo shop, but I guess it will be more expensive anyway & I'll never get my moneys worth for my Kenwood.