I've got the air con from a japanese K10 if you want it.. it would probably be quite a lot of work to fit it, and I'm not sure what you do about getting it re-gassed or whatever.. If you want it e-mail me, mike (at) mikerandall.co.uk
Regarding the power loss.. Dont quote me on this as I havent looked at it for ages, but I've got a feeling there is a little clutch on the bit the drivebelt attaches to, so when its turned off it doesnt really make any difference to power/fuel economy. I may however have just made that up in my mind, I'm not sure, Ed would know as he had aircon on his first March Superturbo..