Trying to compare the 77 - 78 De Rosa and Kessels frame details is not easy to do. The most reliable indicator is the bottom brackets of the respective brands. I have several examples of both De Rosa and Kessels from 1973 - 1978 and I make the following comments: 1. The fork tang you have identified as being used by Kessels has also been used on the majority of De Rosa forks that I have in my possession. Only one of my circa 1978 De Rosa's uses the fork tang variant you have identified as De Rosa. The remainder appear to be identical to your Kessels picture. :( 2. Seatstay termination at lug - Kessels used several frame builders and they used a variety Seatstay termination at lug styles. One Kessels style is very similar to that shown for your De Rosa albeit not quite as long as De Rosa's termination length. My 1978 De Rosa has a more elliptical style as per you have shown for your Kessels Seatstay termination at lug photo. Once again, the De Rosa is larger in length with the the Kessels lug being approx 36 mm vs 46 mm for the De Rosa lug termination. 3. The Seat stay lug you have pictured for the Kessels is very similar / identical to that used on 71 - 73(4?) De Rosa frames. 4. The Kessels fork crown that you have pictured does not resemble any examples that I possess. Mine are all flat at the top with the compass symbol embossed on the top of the crowns. Kessels did supply different fork crowns however and your pictured example may be one of those. 5. Brake bridge lugs - My 78 De Rosa has the same brake bridge lugs as you have shown in your Kessels photo. So, in summary, looking at the bottom bracket is the best place to start when looking at frames of the articles vintage. :)