As the memory of cleaning out hundreds of spammy comment posts is fading, and a large task looms (exporting old blog entries and importing them to a new tool that may suffer the same spam-bait problem, or writing/modding my own spam-resistant custom blog code), I'm reconsidering my plan. I shall try out the new Pivot upgrade.
I've updated now.
There are a few things that seem wrong, like the archives having missed most of what they should include, but it's working and comments should be enabled now.