After bugging people for an hour or so, I finally tracked down svu in #freedesktop to ask about my XKB issues. He got them figured out in probably 30 seconds.
Here’s the final setup to emulate the old en_US with my itouch keyboard and a compose with my menu key:
Option "XkbModel" "itouch"
Option "XkbLayout" "latin" #this changed
Option "XkbOptions" "compose:menu,lv3:ralt_switch" #this also changed
The changes were layout from en_US to latin, and adding the lv3 section to options. I never would’ve thought of trying latin; I figured it was some permutation of ‘us’ I was messing up. And the option is also quite obscure to me.
Thanks, svu! I don’t have $4.99, but hopefully this is good enough. =)