I like the rims! lol...I have 235/60/14 BFGs on mine now as I couldnt get the 245/60/14 Road Huggers anymore, you can add PMD centercaps to these...check my picture
the missing center part buy from Ames...you can get dipstick from Ames too... http://www.amesperf.com/ ....it doesnt need a hood tach unless you want one...betcha Ames has one too!
rear spoiler is a Camaro item ,so is the front, but many Firebirds have them/had them...they DO help, they are functional, esp at speeds over 80- mph....
looks like a great find...as for the tank....there are places that clean these...I`m not sure Id put stuff in it to 'liner' it...I had that in an old Studebaker (someone else had done it), it started coming off the walls of the tank, not good...Id have someone professionally clean it ,IF it needs it....get it emptied out shine a light into it (electric! lol)if rusty ,get it cleaned , it can also have pinholes in it if rusty (that will come thru when cleaned (had that in my old GT6)...so maybe you need a new tank..Classic and Ames sell those...