I want to buy a 86 Grand Marquis can I use it.

You can look at the batteries or look them up at Walmart or a hardware store. If the same sizes are listed for both cars, they're the same. Don't waste your time trying to save a muffler. You'll have it destroyed by the time you get it off. New exhaust parts aren't that expensive.

For steering and suspension parts, Ford has always had a real big problem with theirs separating leading to loss of control and crashes. Don't even think about installing used parts. New ones aren't that expensive from name brand aftermarket suppliers and they're almost always much higher quality.

For trim and things like the steering column, use a "Hollander" guide. They will list every part with a code number. You look that code number up in a second section of that book and it will list every car that could use that part. Salvage yards all use those books and they can tell you what interchanges, but remember you're wasting their time. Most of them will be happy to help you as long as they don't have other customers waiting. You can find Hollander guides on eBay too, often for less than $100.00. That's a tiny fraction of what they cost new.