Aren't the 4.0 and 2.9 related somehow? I'd think that would be an easier (and more fruitful, powerwise) swap.
__________________ Currently 2001 Explorer Sport 4X2 Auto Black/Grey - 100k & still kickin' Formerly 1993 Ford Aerostar Sport 3.0 Auto 2wd Standard length - Light metallic blue/grey 2 tone - RIP Transmission after 160k.