The gauges are made by Stri. The plastic housing was purchased off an ebay seller in the UK. It is designed for installing gauges in a VW, but it conforms to DIN dimensions, so is usable elsewhere too. It is a single piece plastic molding and is very nice.
http://cgi.ebay.com/DIN-Pod-Rack-Headun ... 33639dac19
The brackets that you see were removed from the OEM head unit. The holes match up perfectly with the tapped holes in the Alpine head unit. The mounting depth and positioning are perfect. I drilled mounting holes in the plastic gauge housing and used short screws and speed nuts to mount it to the brackets.
The OEM radio brackets have 3 holes each, one for alignment and two for screws. I did have to elongate some of the holes slightly to get the alignment with the radio bezel just right. With the head unit, you leave the trim ring off. There are no noticeable gaps between the head unit and the bezel, and the faceplate comes on and off normally.
The gauges are a press fit into the plastic housing. Very tight, so they are not going to move. I did have to file the sides of the trim rings slightly to get the gauges to clear each other in the housing.
Not shown: I mounted two relays on the back sides of the gauge housing. One allows the head unit to work with the car's radio dimmer circuit, and the other allows the volt gauge to get a reading directly from the battery side-terminals (for what it's worth).
Here is the sender for the fuel pressure gauge.