Bicycle Mechanics - Replacing an internal hub

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!

are the old wheels steel or alloy? you can't find a decent prebuilt wheel/set that will work on the bike?

the axle will fit the dropouts right? not the spacing as noted above but actually go in the slots?

Sounds reasonable, especially if you do the work yourself. It would be pretty expensive to pay someone to do it.

axles same length?
Probably need different length spokes , unless hub flange diameter and the width of the flanges apart are identical ,

But other than that , since you are getting another drum stopper that should be fine ..

people have reduced the width by changing the spacer/nut combo on the left side.

Thanks for the input. I am not yet discouraged! The axle is indeed the same diameter, so it should fit in the dropouts. Is there a downside to changing the left-side spacer/nut?

You have data on the overlocknut width distance of the 2 hubs in question?

people have used much wider hubs in narrow dropout frames
like fitting Sturmey 8 speed hubs in Brompton rear ends by shortening the stack on the one side it's possible .
then there may be some 'dish', re-centering the rim as the center line between the hub flanges is displaced
from under the center line of the rim ..

Rod brake likely replaced by a cable operated brake .. simple enough housing runs from handlebar lever
to the stop on the hub..