Camaro Rear End Axle housing bumper

[ZLP955]

The rectangular hole has rolled over edges, something is just not right and why the 2 unthreaded holes on each side?

Because there were two types used, a push-in and a bolt-on type (see AIM extract above).

[Z28Project]

I had to put a new one in my car and it is HARD to get in.

Follow what Bentley said for installation and it will go.  I sprayed mine real good with silicone spray, got one edge in as good as I could, and then used a big screwdriver and a hammer on the other edge to send it home.  It is more difficult to get it to pop in than you would expect.

[KurtS]

Use dishsoap. That's what GM used.
Keep the silicone away from the car - it will screw up paint (new painting, not existing paint).

[Boston14]

That is exactly the way mine is on my 11D (early 1969)  SS-RS convert.  Just forget about the holes on either side of the rectangular one you can't even see them with the bumper installed.

[marriest]

That is exactly what it looks like.