I have enlarged holes in saw blades as follows:

First I clamped them in a vise carefully avoiding the teeth in the jaws.

Second I used a tapered reamer to enlarge to almost correct size from
both sides.

Third with leather gloves and a strong leather or canvas apron I use a
three cornered machinist scraper to enlarge to finished size while
rotating the blade by hand.

I have done this on several blades with good results.

CP