broken key in chain drive gear on crankshaft

[work_in_progres]

Greetings:

I have somehow been suckered into helping my brother with the re-assembly of his 91 560SEL after a botched chain replacement.(Yes I admire him for trying), but explained to him that beer drinking(with friends) and engine timing chains is not a good nor productive way to go about this amount of work.
He has proceded in breaking a chunk out of the front chain cover(from prying it off(over the phone I tried to explain that prying on aluminum sealing surfaces is never a good idea). It appeared that the oil pump chain was holding the chain cover on, and after removing that the cover was free to be replaced in the recycle bin.
The issue I noticed was that the crankshaft key that is keyed thru the chain gear(on the front of the crankshaft) and front hub(also keyed to the crank)is sheared/broken off very close to flush with the chain gear on the front of the crankshaft.
Is the toothed gear removable? If so, is there a recomended tool to facilitate removal at the home garage?
Thanks