It wouldn't be terribly difficult to design a fixture that bolts into the main bearing web in question that would guide a flycutter to do the narrowing procedure, but unless there's a lot of demand for the tool, it would take a long time to recoup the cost of making it. It would be fairly simple to fabricate- - - -something that holds 3 or 4 replaceable carbide cutters and some sort of depth-of-cut jackscrew to control how much material gets removed. The tooling could be driven by a variable-speed 1/2" capacity drill motor.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!