After fiddling about with it in private for a while, I’ve put a custom theme on notes.husk.org which matches my main site. More or less.
Annoyingly, Tumblr doesn’t provide title fields for all its post types, so I’ve used the post ID (which crops up in the URL) instead. Hopefully this works. Sort of. It also seems to provide only minute-level resolution on its timestamps. Eh.
The design still needs some tweaking for spacing (on photos especially; ideally I’d also align them to 16 pixel boundaries) but then, if there is anyone reading this, they’re probably doing it via RSS or the dashboard. So nobody will mind.
Now you may go about your bufiness.