I have Red Snappers and I believe you could use a saw to cut them to length. However they do come in sections so you might not need to cut them. I love my Red Snappers. At first they are very tight but loosen a bit with use.
Leaders with markings are helpful in centering your quilt and keeping it straight. That being said, you could buy heavy weight cloth and using a permanent marker, draw a straight line on it and mark the center. Or you can buy extra long tape measures that you can attach (sew) to your leader cloth. Check out Erica's Craft & Sewing online for long arm accessories. She carries long arm tape measures.
Attaching a leader to the rail could be done with sticky back velcro - that is how mine is attached.