As far as I remember, I used the donor springs and did weld a new perch and shock mount (shown). I also used the donor shackles and hangers and did a shackle flip, but I was doing 4x4 under it. (That's a whole 'nuther post). You just need to take off the old and start mocking up the donor to plan your attack. I personally would not use and old 3.90 rear end. Why are you doing a T5 and all this for a 235 motor? Are you looking mostly for mileage/gas savings? Don't get all wound up on gas mileage. If you are wanting mostly cruise speeds like 65 MPH or higher, a 3.90 is not for you. If you like shifting a bunch with a 235 6 cylinder, that's fine but did you ever consider a 700r4? or other AOD?
