ISO crusty mechanics with cottered crank skills....

Pulled my first set of them last week and mushroomed the cotters upon removal. I'm really not keen on a. finding a new set of cotters, and b. filing the flats to fit, so I'm wondering if I have options for making things work. As it stands, I can't thread the nuts onto either cotter. Can I clean up the threads (I don't have a tap and die set)? Can I dremel off the mushroomed part and expect a nut to thread onto the cotter (there is enough room to do this)?

Thanks for the help.