if your car is a TI it already has a blow off valve on it. its located inside the air cleaner box so you cant hear it when you shift.
look at the hose going from the turbo outlet to the throttle body- you will see a 3/4" size hose teed off from there that goes into the bottom of the air cleaner box. inside the box attached there you'll see the blow off valve. if you want more sound out of the valve you can remove it from the air cleaner box and relocate it out in the engine compartment. just cut the hose off where it tees off the turbo outlet hose, leave about 3 inches and reattach the valve there, run the vacuum line to the nipple on the throttle body and you're done. make sure to use hose clamps of course.
since the previous owner liked to "fix" things i would go over the car completely, especially the vacuum lines. i would highly reccomend replacing all the vacuum lines and installing a vacuum block if the orignal plastic one is gone. do not use rubber vacuum hose, at autozone and the other parts stores they will have the black plastic hose like what was used from the factory- its packaged in the Help! line and sold as "emissions hose" by the pcv
valves and pcv
grommets. you may also want to get the little rubber boots that the hose attaches to, its in the vacuum tee section, those tend to dry rot and leak as well.
if the tires are flat spotted and you've already blown one out i would just preplace all 4 of them and call it a day. last thing you need is a tire comming apart on you while you're going down the road. besides you can get 15" tires pretty cheap if you do some shopping around, 205/60/15 would be the factory size on the 15 inch rims.
edit- 87 TI right? it should have the log style intake- throttle body is attached directly to the turbo inlet, correct? if thats the case ignore the bit about the BOV
above- your car wont have one. if it were my car i would swap out for the blow through style intake, the log manifold pull through style intake, well sucks. 88 up turbo cars will have the blow through style intake manifold, get the throttle body as well. add that with an intercooler, the stock one will work great. a TII mopar stage 2 computer to finish it off will REALLY wake that car up, you think its fun to drive now....