I actually did a little more than thinning on this frame's lugs during its restoration. I also enlarged a few of the cutouts with a diamond-tipped Dremel burring tool. This was done slowly and carefully over a period of about a week. When I was done removing steel, there was still brass residue underneath, so I know I didn't get down into the tubing.

The lug window below was much smaller than it is now:

http://farm5.static.flickr.com/4119/...9edc3e94_b.jpg

DD