Will the fender skirts from a full size 70's Eldorado fit my '76 DeVille? I've only seen on ebay and can't really tell from eyeballing it. Does anyone know?

I really doubt it. In my experience they are pretty model specific. I did see a Caddy recently that looked like it had the wrong skirts on it. They didn't look right to me but the owner must have thought they did.

No. The skirts follow the contours of the body panel, and the panels on the 71-74 Eldo (only ones with skirts) do not match those of the 71-76 C-cars. However, the skirts from any 71-76 C-body Cadillac will work. Look about for a set of those.

Craig