I'm researching for a project and on the subject of 41mm fork tubes it was recommend that I have a look at aftermarket fork tubes for H-Ds as they're available in many lengths over and under stock length. I guess stock is 24-1/4" right?
While bopping around the interwebs I found a forum post that suggested that the 41mm fork tubes on Harley models are actually 1-5/8" or 41.275mm and will not interchange with actual 41mm forks from other bikes.
I've found that the 1-5/8" forks began in the 1940s and were used into the early 1970s when front drum brakes were replaced by disc brakes and on until present day. Was there at some point a change to true 41mm tubes? I can't seem to find confirmation one way or another.