I will start with I am not an attorney, but have some experience with intellectual properties. The design is great and I can see why you all like it. The issue is that all art has what is known as an implied copyright when it is drawn and the artist can file a copyright at any time. If you wish to use this art for any purpose you will have to establish what is known as prior art in other words you had the design first. Sale or distribution to the public, no matter how limited is considered a copyright and or trademark infringement.
The next issue that is of concern is the use of trademarked logos like the Grateful Dead Skull and the Yamaha tuning forks. These are registered trademarks and are only reproducible with a license. They can sue for the unlicensed use. In a case where there was no mass sale or distribution, there probably won't be anything more than a letter to cease and desist from an attorney, but they can sue for damages to their trademark. Sorry to be a wet blanket, but would recommend you proceed with an understanding that there could be some issues down the road.
Again, I am not an attorney so you may use or rely on this information as you wish. It is accurate to the best of my knowledge. Does that sound like one of those adds with the rapid fire disclaimer at the end.