I have seen this several times. the way I repair it is to drill it out
with a "left hand" drill bit.  Usually the fitting does not come out.
But get as much out of the intake as possible without damageing the
threads in the intake. This takes alot of care. The threads in the
intake are pipe threads. Take the new fitting to a plumbing supply
store to match it up. Sears/ Lowes/ Home Depot don't sell that size,
Been there, done that. As for the filings falling into the engine,
after removing the old fitting I stick a garden hose in the filler
neck of the radiator  and turn it on. the pressure forces most of the
filings out of the fitting hole. the few that remain should not cause
any problem. Before you do this make sure you drain ALL the coolant.
this way you wont be flushiing coolant all over the place. I hope this
helps.

Any good auto parts store or tool truck will have the extractor for
this.  A little metal in the cooling system is not the end of the
world -- very different from metal in the oil.

Don
www.donsautomotive.com