I'll take a pic later. The holes are already in the scuttle corners, underneath where the screen sits. The drain is a small, tapered white tube that pushes into the hole. There's a pvc hose on the end that disappears into the A post, I assume to the bottom, so that water that gets behind the screen seal, drains away rather than sitting in the corners or running over the lip and inside the car.
I think the problem is, because the drains sit in a hole, eventually, the steel rusts around them. The last owner of mine repaired the rust and covered the holes. All good, except now, water gets inside and sits at the bottom of the screen aperture and rusts that too! It's all just part of the fact that in the days of the Cortina, they were never intended to last this long! ;)
You won't see yours unless you take the screen out. Once removed, I would agree you're on a hiding to nothing trying to feed the tubes back through!