I presume you mean the oil sending unit, which is what drives the oil pressure gauge on your dash?
If so, I know on my old 1985 straight-six it was a bell shaped housing, about 2-1/2in tall by maybe 4in wide (rough estimate) that screwed directly in to the side of the block, about in the middle on the non-intake/exhaust (drivers) side.
Here's some pictures from J.C. Whitney. These are just generic sensors, not necessarily Ford sensors, but they should help you get the idea.
All Ford trucks '87-up DO have a pressure "switch" from the factory. Not a sender. '87-96 have a resistor on the back of the instrument cluster that causes the gauge to go to mid-scale any time the pressure is over 6 psi. '97-up have no resistor - the gauge itself is built to show mid-scale when the signal terminal is shorted to ground.
Regardless of switch or sender, the 4.9L block's oil pressure port is where mrainey described: #9 below.
The captions of these pics describe how to convert from the newer switch to the older sender. For a straight 6, you don't need the plumbing - just the sender & the jumper wire.