With the new display items in Minecraft, you can now make a block out of 8 player heads. This website will turn a block texture into a set of 4 player heads that will be used to display a full custom 16x16 block.
Use default image as template, create and upload desired texture.
Upload each skin one at a time and fill in the form in step 4 as you do so. If you wish to upload them to the head database use a name like "Cobblestone Multipart 1"
By default, the coordinates will be the block directly above a command block.
If you find any bugs, you can message "daisyeseyad" on Discord.