Packaging Anki for Slackware

I use Slackware (not a systemd distro), and would like to update the current Anki SlackBuilds script (which doesn’t work for anything higher than Anki 2.1.15) so that it can package Anki for Slackware.

However, SlackBuild scripts themselves are not permitted to download anything. I can download Bazelisk and the Anki source before running the SlackBuild script, but what else would I need to download first so the SlackBuild script can handle everything without downloading? Also, how can I do non–in-place builds of Anki?