88 ranger gt help

I couldnt resist this little truck for free.But it needs alot of work.I pulled out the seats so I could take the carpet out and clean it.There is a silver box under the passenger seat that I have no clue about what it is.I am guessing it has something to do with the radio.Amy help would be appreciated.I would also like to know what performance stuff is out there for it.I already have a set of pacesetter headers for it and a cai,but was thinking of a bigger throttle boby.