Hi Dan, from my understanding of snap line square rule, you need not drop lines down the butt ends which means you do not need to level the timber side to side or end to end.

You may instead take the wind out of it by placing a stick in the center of the timber, a level can be used but does not have to register level, it is only to sight to. From one end lay your framing square on the top surface with the tongue hanging down. With a shim, shim the body of the square so it aligns with the level at the center of the timber. Now, gently slide the tongue to the side face of the timber until it just touches at some point on the side face, it may or may not appear square. Now mark 2" on the top face and the side. Without moving the square focus on the other face. Place another square, use the 2" body as you are using 2" references, up so it just touches the top square and mark 2" on the opposite side. You now have 2" marks on 3 faces. Repeat this on the other end. Don't forget to mark the center where the level is setting, trace a line on either side and X it out so you can refer back to it if need be. Snap your lines connecting the respectful marks at the ends. This really only takes a few minutes to do and you have straight lines to work with.

As for the tie, what I do is saw the natural curve with my band mill, as I feed into the timber I follow the natural curve of the timber by raising and lowering the band through the cut. This gives me a flat surface to use. I then snap lines as above, with the timber laid on the side, using the typically wider face as the first, best face. There is a slight deviance. This helps not much for live edge stuff. If you are not scribing the braces in then you will have typical square rule housings, depending on how round the live edge is, the housing will come into the side face, assisting in the layout. A combination of squarers will get the pocket laid out. The next question is how it is cut? Live edges are different but I feel as if I don't have the time to deal with them, heavy wane is bad enough.

You could hew off the live edge, too.