Pretty sure that the file on the sidekick is just 420HC at < 58 Rc... it's really short and rather soft, so it would take you a long time to maybe slightly dull the edge of that spine while significantly dulling the teeth of the file

Nah, skip it. Get a coarse hone - SiC, diamond, etc. - and use that. In fact, if you want to wait, I'll do it to my new-spec 5.1 using a cheap hone and will report back tomorrow.
Oh, and congrats, by the way! I've been out of town / internet access and missed out on the fun of you getting your 4.7 duo