Try this. Add all the HTML files into a zip file. Add it to calibre and convert the zip to ePub. Get the program called Sigil and open the ePub in Sigil. Rearrange the files into the order you want. And save. Add the saved file to calibre and convert it to mobi.
While you are in Sigil you can creat h2 and h2 headers to creat a TOC.
Welcome to MR freewheeing. Did you forget your L?
