Michelle taught her printers a really nice, simple registration system. They were printing 10-15 layer relief prints with this that looked flawless! She said it is better not to add white ink to a relief because if you use miracle gel instead, the colors will have more unity and the white of the paper will provide luminosity. White will make it look more graphic.
The backing is chipboard (although I think any sort of MDF would work fine, chipboard is just really cheap). The punch registration pins are taped at the top with enough space left for a border. The board is covered in packaging tape so accidental ink can easily be wiped off. The linoleum plate is glued in the center with tacky glue. It stays attached during cutting and printing. The plate sits higher than the pins. They used Gold Cut Linoleum (it cuts easier even if it doesn't hold a line as well as some others) and pins that were .070 in height.