drum to backing plate interference ??

Well I found the problem.

It dawned on me that I have an old used pair of 11" drums out there. So I got 'em and they fit perfectly. No scraping, and they sat flush against the axle face.

So I measured them. From the rear edge of the drum to the front face of the drum the old used drums (ones that fit) measured 4.495. The new drums (ones that don't fit) only measured 4.390. There is about .100 difference between them. You can see the gap on the calipers on the new drum.

Also the cooling fins go about a half inch higher on the old drums. I guess I have to figure out what the heck these old drums came from and get a new pair. How in the world am I going to figure this out!!??