Graham, Check this link,
http://www.opelgt.com/forums/showthread.php?t=248&page=3&pp=15&highlight=alternator, and my post #40, and you will see how I did mine. The upper bracket you will have to cut and drill out for the hole, but I've had no problems so far and it all works. I did later go back and added a terminal block and relays for High/low beams, fuel pump, and fog lights. I got the relays through
http://www.madelectrical.com/index.shtml. A little pricey, but everything is included, wire, fusible links, connectors, heat shrink tubing. Local auto parts sell relays as well, cheaper. I didn't want to take a chance on melting down the fuse box. Jarrell