Best but not easiest is to grind off the rivets. I don't like to have excess pieces on the undercarriage, they always seem to get in the way, draw blood, etc - the new crossmember bolts to the frame.
I'm not sure on the E-brake. I've only done the Saginaw swap on a pickup, the brake cables weren't a problem there. The new crossmember, though, is much less bulky than the box-section original, so you should be able to work around it. If someone else has some direct experience with a car installation, please help us out here.
Before you get too deep into this, do you know which Saginaw you have? The number of rings (or grooves) around the input shaft splines are the key to what the internal ratios are. Some are better than others.
