Well, a few hours ago, after taking a second try, I finally got the SDKK to install.
I did it by removing all non-Toxikk content and scripts from the the UDKGame content and script directories, AND FROM BOTH workshop directories, as if I had never subscribed to any workshop item or downloaded any mutators or maps.
Only after I did this did the SDKK install without crashing first.
It wouldn't have even occurred to me to do this except I saw in the logs the SDKK was failing to load from Zedek's wl4objects, so I saw I should get non-Toxikk items out of the Toxikk folders. Thank the Lord for this or I would not know why it was failing.