Is there a way to remove the top of this barrel?
Then, based on your comment that you only need the lid as a dust cover, I would cut around the top of the wall as close to the lid as possible.

Once separated then remove any excess on the lid to leave a slight taper to help the lid "sit" neat after.

I have cut these with a hand wood saw before, a bit boring but the plastic usually cuts well. I found a jigsaw too "bouncy" and it would not be close enough to the lid.

I did 8 of these barrels for my parents for rainwater and made a tool on a broom handle to hold the nut &amp; washer to screw the fitting into so the two original holes were fine, no need to take the top off... Depends on what your fitting is I suppose...