Frame rivets wont come out

[82Cecil]

Slowly moving along with my lowering project.

I ground down the heads of the front spring hanger frame rivets on the rear leaf springs, thinking I could use an air punch and pop the sheared rivet through the hole.

NO GO.

The rivets seems to grab the cross section of the frame it passes through.

I am thinking now, progressively drill a larger hole through each rivet until I can easily colapse each one. My priority is preserving the integrity of the frame.

What is the best way to finish this job.

Thanks for your help.