I had a slightly different problem installing these mirrors on my 1931 Coupe. The pin that comes with the kit is 1/4" diameter. On the drivers side I was able to remove the top pin rather easily with a nail set punch and hammer followed by using a length of 7/32 rod to complete the removal. The new pin installed easily and worked great. Remember to support the rear of the open door while doing this because the weight of the door will un-align the holes in the hinge parts due to its weight when the pin is finally removed.
Now on to the passenger door. Pin removal was a little more difficult but finally succeeded. The top of the pin was knurled. Then the new pin would not fit, too big. Measuring the removed pins with a micrometer revealed that the passenger pin was indeed slightly smaller in diameter. Apparently one side of the hinges had been replaced at some point in time. I had to mask off the paint around the hinge and drill out the hinge using a long 1/4" bit and drill. That solved the problem and the mirror got installed and thankfully the door is still aligned. If I ever remove the mirrors I will need to obtain a new 1/4" pin from Snyders,