Good going. Everyone swears by the M-600 series Dursts. I had an M-601 years ago and loved it. Yes you can use that carrier for smaller negs, if it has adjustable mask, or make your own mask. Depending on the lens, you may not be able to get big enlargments with smaller negs., because of the telephoto effect of the larger lens. Sounds like you have a good start at getting your DR started.

Rick