I installed clear corners on my 300E with no problem at all, they just snap in. Make sure that they are in the right slots though, you don't want to break the pronges on the lens.
You mentioned drilling? Are you sure you're talking about corners and not side markers?
My fault you did say side markers. I thought about this also but stopped for fear of looking like an idiot if they didn't come out right or looked ugly.

[This message has been edited by rich30769 (edited 07-21-2000).]