Looking at the diagram on my dealer service manual it seems that the location of the oil pump drive will require removal of the motor to access it. The manual does say to remove the engine for camshaft replacement.
6. Remove the hold-down clamp (12270), screw and oil pump drive shaft (6A739) from the rear of the cylinder block (6010).
NOTE:
California Ranger and Explorer vehicles have a CID sensor mounted on top of the oil pump drive assembly. Sensor Adjusting Wrench T94T-12270-A is designed for easy access to the hold-down clamp screw.
I don't know if the wrench mentioned above will allow you to get at the bolt without removing the whole engine, but either way I looked up that tool and it seems to go for $70-90 online.
EDIT: Also, there are several forum members who have changed their cams but you will have to do a forum search to find their tales.