The Rover-Landers of BC

I was driving down the street when there was a loud grinding noise, along with a loss of power. I pulled over and there was a screw sitting on the block next to a screw hole that has oil splatter all about it. I got home, checked the manual and its a cam follower guide locating screw. The screw itself does not appear to be original, but rather a regular screw ground down to the necessary taper. I cannot get the screw back in far enough to engage the threads, so I think the guide has slipped down. Has anybody had this before? How bad is it? How far apart does the engine have to come to fix it?

jeremy