I don't recognised the serial format, so based on that and the AC9 start I'd take a guess it could have been made in 1999. If so, that opens up more possibilies as there were more aluminium models in the range by then (Arrowhead, Terramoto etc.)
I mainly ride 175 mm cranks. I have some 180 mm to try, but I haven't actually fitted them to a bike. I have one bike with 172.5 mm where I notice the difference, but I'm used to it now. I've previously had come bikes with 170 mm fitted and it I rode them a decent distance I'd start to get a...