Edit: as many have already observed, one of the books is an orange-spine version of Fiend Folio. The interior of this book was easy, it's just a PDF of the original (though I did have to straighten some of the pages and improve the contrast for print quality. The work went into creating the cover. It uses Jeff Easley art that was originally intended for a version of the Fiend Folio, which they ultimately decided not to go ahead with since FF was the lowest-selling of the 1E books. It was printed at Lulu.
I got the idea from someone else who did this some time ago, there are posts about it online. But it also led to the second book, which I'll detail in the post below.
Edit: after doing the Fiend Folio, I got the idea to do Unearthed Arcana II as well. This one was way more work. The cover was easy this time, since I already had the template from FF to work with. Just got a scan of the art of Encyclopedia Magica Vol. 2 I believe it was.
The interior took a long time. I took various articles from Dragon magazine and adapted them, focused on presenting the 2E classes that Gygax had talked about (jester, mountebank, mystic, savant). I also adapted the bard into a regular class. There's a whole bunch of spells borrowed mostly from Oriental Adventures, and there's a few things taken from some modules (the Conan modules and Lankhmar), since the sales text for the cancelled UAII suggested that some info would be taken from published modules and Dragon articles. And there's a bunch of stuff from some of my favourite Dragon articles from back in the day. I did the layout using appropriate late-1E fonts, and took illustrations from Dragon articles as well. Many, many hours or work went into it.
I put Kim Mohan's name on it since I figured if the book had been released, he'd be editing the material, though I must have assumed that Gygax would have been out the door, otherwise I'm sure he would have wanted his name on the cover.
You might be able to tell that this cover is glossy, while the FF cover is matte. Makes me wish that Lulu had a semi-gloss option, since the actual 1E books are not as glossy as this, but are glossier than the FF above.
I was browsing tsrarchive.com and came across information for a cancelled 1986 AD&D book - Unearthed Arcana II. They include text from the 1986 TSR catalog: "A new hardcover compilation of new rules, character classes, and exciting adventure options, following in the tradition of last year's...