I have a 1999 f-150, 4.6 engine with a 5 speed tansmission. I need a lower ratio reverse for backing up a trailer.The 5 speed transmission in the truck is geared too high. One idea is to swap out my 5 speed for a  zf 5 speed transmission from a f -250 that come behind one with a 5.4 engine, (these trans have a lower ratio reverse). The question is will this transmission fit in a f-150 chassic behind my 4.6 engine. Anyone with help would be appreciated.  

The bellhousings should be the same from the 4.6 to the 5.4.  The 5.4 is just taller.  It should work.