FWIW, there was a nice early car with a home-installed DOHC 5.4 at the '09 Reno Fun rally. It appears the 5.4 is easier to install since the taller block causes the gigantic heads to rise up over the inner fender panels. With the shorter 4.6s (any variety), notches must be welded in the leading edges of the inner fenders and small pieces sawed off the heads for clearance.
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