I did M51 on April 22, 1998, same film (even the same emulsion number), exposure, optics, etc as in my comments on NGC 2403. My tracking was perfect this time, so my star images are rounder than yours. My limiting magnitude is clearly better than yours, but perhaps this is due to your mistracking. The big difference is in the color. Yours looks like it only recorded blue light, except for a hint of red in the companion galaxy. In my print, the two galaxy cores are clearly yellowish, while the spiral arms look purplish, due to the mixture of blue stars and red hydrogen gas. I greatly prefer the color of mine, but then it might not look as good if it were scanned.