Got it working with less than 10 minutes to spare. Artist says it works for his sideloader which apparently isn't SideQuest, but I recreated the issue (endless loading and eventually the apk doesn't respond) and found out it was a single tickbox (for distribution) that needed unticked during packaging to fix the issue. Should work with SideQuest now but the upload is taking FOREVER. Might not make the deadline. Upload started at 4:28pm EST.
UPDATE: Still not working with SideQuest, for right now installing the .apk through Oculus Developer Hub appears to be the easiest solution.