What are you going to trim on the non-SFI bells? There's nothing there.
The ones that need trimming are the SFI bells with the 1" of extra flange hanging down, where the bellhousing bolts to the block plate. That's the way the Lakewoods were made and what is being referenced in a lot of the car assembly manuals.
Big difference.
http://www.jegs.com/i/Quick+Time+Bel...6-SFI/10002/-1
http://www.jegs.com/i/Quick+Time+Bel...-6056/10002/-1
The Lakewoods are larger bellhousings in many different dimensions, especially weight.