The Super Sprag or the equivalent Ultimate Sprag seems to have more holding power to me. And the design looks like it is less prone to being "rolled over", losing the springs and rollers (failure).

The low band apply valve body will help protect the sprag. In 1st gear, the sprag holds the rear drum from spinning. With the low band applied, it also holds the rear drum.

Both the low band apply valve body and the improved sprag are good ideas, but I would put the LBA valve body 1st on the list.

An aluminum or aftermarket steel front drum is a safety item. If the sprag does not hold, and the low band is not applied, the front drum will spin about 2.2 times the engine rpm. And that can easily make the stock front drum explode.