What's the spacing on your rear dropouts? If they're 130 mm apart, you're good - you can just get something like a 10-speed Shimano 105 hub and put an 8 speed cassette on it, assuming you have downtube shifters - just use them in friction mode. You can keep using your 7 speed chain with no problems.

And if you have a steel frame with 126 mm dropouts, it's not hard to spread them 2 mm on each side.

FWIW, if you're looking at Mavic CXP33 rims, also look at DT Swiss RR 585 rims. IMO the DT Swiss rims are a better rim - the machining of the brake tracks is smoother, and the DT Swiss RR 585 is just about the strongest narrow road rim you can find.