Plumbers putty. It was used by GM between the hood hinges and the cab to keep rain out of the cab.
Personally, I would worry about filing on a chromed piece of pot metal. I am concerned about opening up pot metal to the atmosphere, leading to corrosion as pot metal is prone to do.

Last edited by 52Carl; 12/28/2017 11:22 PM.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission