Had a 66 with headers......couldn't get the motor out with headers on......pulled the entire front clip even and it wouldn't come out. Didn't try loosening the bolts, but if I remember right it wasn't even close to coming out. Simply couldn't get the motor high enough before it hit the in the back.....but the headers wouldn't clear the front crossmember. If I remember right the headers would only go in from the bottom, even with the front clip off.
Not sure how valid all this is with a 65 though
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