IIRC on the Capricorn (nearly identical mast profile) 25 is the setting used for very light winds, in high winds its somewhere in the 30-35 range.

Spreader rake is usually around 50mm, maybe 60+ for light crew and/or heavy winds, this is measure by laying a batten across the wires at the spreaders and measure the distance to the mast track (i hope you meant 80mm and not 800mm <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" /> ).
Rake is indeed adjusted by change the length of the arms (make sure they are at identical lengths).

Hope this helps.