I have a Dutch three speed (Gazelle Toer Populair) that I want to convert to a five-speed. Simple enough? At present, the bike has a Sturmey-Archer AB hub with a drum brake that is rod-activated. Sturmey-Archer makes a five-speed wide-range model with the same drum brake setup -- the XL-RD5(W). My idea is to replace the old hub with the XL, using the old rim but essentially building up a new wheel.

Any unforeseen headaches anyone can see? I know I'll need to have the frame stretched out in the back by about 6 mm on each side. Anything else? Am I crazy?

Thanks!