As I mentioned earlier, De Rosa was still doing plenty of custom bikes and pro bikes in that time period - but the decals (at least the one on the HT) are just plain wrong.
Edit: By "wrong" - and this goes to Old Fat Guy's last post as well - the diamond shaped World Championship bands on the headtube decal don't appear before about 1978-9. The bike should have the red scroll decal as in Caterham's last post. They just wouldn't have been on a bike with the long Campagnolo dropouts, unless De Rosa did something really unusual in terms of the build. In other words, I don't think "custom" accounts for a decal style at least a couple of years in the future, in this case.