Well here's my opinion....
If it's knocking that bad, the crank is probably shot as well as rods needing to be reconditioned. 140,000 miles (usually hard miles) is average for these cars it seems when beaten on. Did headgaskets go recently??? This is usually the demise of the bottom end when the gaskets go.
Anyway, Ford offers a long block SC motor for just under $2000 retail. This comes with a 3 year, 50,000 mile warranty. Complete bottom end, heads, little hotter cam designed by Ford for the V-6 stang (works great in these cars!!!!). I have personally seen four people here in Jersey get them and are extremely happy with the results.
To me, the selling point is the warranty. Also, you might be able to talk to the wife and convince her since it is warrantied and "look honey, a new car doesn't come with that" deal.
Well, good luck and don't part her out. As they say on Hot Rod TV "Don't crush them, restore them."
Don