Yes definitely take those bolts out asap!
On the drain... in the past ive used a 1" piece of sch40 inside of a 2 or 2.5", and poured the gap with epoxy. A standard bronze drain will fit right in the 1" and the screws will be going into epoxy, leaving the core totally out of the equation. Holesaw out the core and leave the outerskin then glue it in. Inner skin will go over it on the inside.
Some guys will just delete the core at the bottom but then youve got screws coming thru the inside usually. Not a fan...
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