He's written a blog post about it on his website (Webomator); here's an excerpt:

     "From right around 1975 to sometime in 1978 I drew illustrations for some of the earliest D&D supplements, modules and fanzines, and even had one cover and two illustrated stories in TSR’s own The Dragon magazine. I also did some of the covers and illustrations for Dave Hargrave’s Arduin rules sets and for a great many products, some peculiar in retrospect, for Wee Warriors; that included the first commercial D&D character sheets and the very first module for the game (Palace of the Vampire Queen). There’s a huge, long and complex history of those products that I frankly don’t remember very well after all this time. But in this age of eBay and the Web it’s not too hard to ferret that history out."

     Some of his work for the Arduin Adventure (1980) can be seen in my 2011 post here.

     And on the Acaeum he writes:

     "So recently I fired up my scanner and Photoshop and worked through the pages of my 1978 "Dice of Fate" portfolio and some other bits and pieces from the seventies, and eventually I ended up with this calendar of old (or, I guess, distinguished) Morno art from 1975-1978.

     I can guarantee that there are some things in here that none of you will have seen; a couple made their only appearance in that portfolio, and a couple are Tolkien illustrations that only ever existed as greeting cards back in the day."

     As a bonus, here's his first ever cover for the APAzine Alarums & Excursions, edited by Lee Gold. This is from issue #11 (May 1976, scan courtesy Hall of the Mountain King), and is not in the calendar, although two other A&E covers are according to the artist (only one has the A&E logo). Issue #11 also happens to contain the very first published D&D article by J. Eric Holmes, Warrior-for-Hire.

     
     The original Arduin trilogy of booklets ("Grimoires", 1977-78) were written by Dave Hargrave as supplements to the original D&D game. The Arduin Adventure, published in 1980 by Grimoire Games, was the first product to present Arduin as a stand-alone game, in an introductory format seemingly inspired by the Holmes Basic Set. According to Gygax, the Holmes Basic Set was selling 12,000 copies a month by mid-1980, so it was natural that other game designers would follow suit. Thus, The Arduin Adventure box set ($9.95) included a 64-page rulebook with all of the necessary rules, three character sheets, two sheets of magic item cards, and two 20-sided dice. The rulebook was also available separately ($7.95), with cover art by Greg Espinoza.

     Much like Basic D&D distilled the original D&D rules, The Arduin Adventure simplifies the Arduin trilogy to six races (elf, dwarf, hobbitt, human, amazon and half orc), five classes (warrior, thief, priest, mage and forester), twelve statistics (dexterity, agility, strength, intelligence, ego, wisdom, charisma, hit points, armor class, mana and experience level), combat rules, four levels of spells for priests and mages, a short list of magic items, and about 30 monsters.

     The rulebook also contains a nine-page introductory scenario, The Forgotten Tower, set in a lost wizard's tower (rather than beneath a destroyed one as in the Holmes Sample Dungeon). It has 45 rooms including eight in the dungeon that are to be keyed by the DM (ala B1 In Search of the Unknown). A picture of the Forgotten Tower was included on the back cover of the rulebook, with art by Brad Schenck (Morno), known for his work on Wee Warriors products, such as the cover and maps for the first D&D module, Palace of Vampire Queen.

     The Arduin combat rules use Dexterity scores for initiative. This goes back to the first Arduin Grimoire and predates the use in the Holmes Basic Set. In The Arduin Adventure, the "Monster" section gives typical Dex scores for each creature, and a few monsters in The Forgotten Tower also have Dex scores listed.