Why?
You're putting a motor capable of towing into a chassis that can't tow what the motor can.
A 7.3 is a hell of a lot bigger than small block for anyway, I'd venture to say it wouldn't fit. And if you got a turbo 7.3 (the CL ad is a non-turbo) the turbo sits on top of the motor in the intake valley so the 7.3 is considerably taller than the 351 or whatever the wagon came with.
Buy an F250 for a tow truck, buy a 300TD for a wagon.
