Brake booster on a 1986 Sun-Land Express, an original part, leaked due to old age; I lost braking ability.  Mechanic replaced both master cylinder and booster immediately.  Had to search somewhat for the parts (particularly the booster, I think), but I now have adequate braking capacity again.  I'm just the owner/driver, not a mechanic, but I doubt I'd suggest 'fixing' a vacuum vessel.   

I would be very careful grinding the lip of the booster. That is a vacuum vessel. I’ve seen them leak just from age.

As soon as you grind that booster, you’ve lost any factory warranty it might have. I know you’re between a rock and a hard place. Good luck.

Won’t pound

id just grind a little should be fine at the lip sticks up 1/4”.. , but may have a 1/4”-1/2 spacer made too. That’s would cause the bolts and rod to be shorted.. def enough rod but unsure of the bolts just yet . I could notch the bolt holes so the booster would slide up slightly.  but that would cause actuation of the booster to be slightly at an angle.. can’t lower the steering column.. a huge job..  Will probely do a comination of all of all of these.