Those cranks are HARD. I hope you aren't thinking of grinding down 4 thousandth of an inch off of one side. I think you will not only kill yourself trying but if you suceeded you are going to compromise the fitment/roundness which needs to be pretty darn exact for the cotter to hold it properly. If there are any high spots or wows in it you are going to have problems.

I'd take the crank to a machine shop and have them bore it out a little bit. They can keep it round. Either that or have the spindle turned down a little bit on a lathe. I'm not even sure doing it by hand is even possible. Like I said -HARD.

I had good luck at my LBS -they had a crank for $5. Maybe yours has a spindle.