Success! I ended up hammering down one side of the slit (after it had been heated up), which gave me enough room to curl it up. Everything after that was simple.
Auburn, yes I built my own tool. I built it using aluminum rod and JB weld (I don't have easy access to a welder, otherwise it would have been welded). If it fails, I'll build a welded version. With respect to tightening the cartridge.. to make sure I understand properly, what I understand is the following: hand tighten the rod (the piece with the 26mm hex nut) until its snug. Only than use a torque wrench (I'm almost going to assume its better/easier to torque the allen bolt and not the 26mm?).
With respect to metal fatigue, I'd like to hope these don't break. This bike has 14.6k miles. The reason for replacement is that the fork seal on the RHS was leaking, so I've decided to replace both sets.