Me being old school, I would have probably just used my die grinder and special tip to radius a new circumfrence. It wouldn't of taken much to make it work
That's 1/4" difference, or 1/8" on all sides. It's unlikely you'll ever get it right with a die grinder.
You can machine down the convertor hub, but you have to stay off the weld or it'll either seperate or leak. I had this exact problem before with a 273 motor I had, and ended up machining the crank hole after having a convertor ruined by a bad machinist.
