I found it necessary to unpack the zip files into their respective areas first, due to poor handling by the engine. If you get many red-text errors in the console at startup, then unpack the 12 zips in data, and the two zips in lbinteriors_custom. If those are not there, you may have had a corrupt download.
Otherwise, if the level still lacks interiors, open the console window, look for any red (error) text in the window, and if it references a missing interior, check your interior folder/zip to see if it exists. If it's another error, please report what it says here.
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