The 3.8L out of an 83-86 mustang/capri/cougar/thuderbird/marquis/LTD/continental is the same engine as the 94-04 3.8L, however there were of course many design modifications done. I don't know how much actually interchanges or swaps, but it is the same engine. As a side note though, this engine is of the 90 degree design and is basically a small block Ford v8 with 2 cylinders cut off. It does not share any similarites with the Ford Cologne series of 60 degree V6's (such as the 4.0L, 2.8L, 2.9L, 2.6L).