I’m glad this question surfaced and in the framework that it is asked in. I imagine this thread will go quite a ways and generate opinions in many directions.
To sum up my opinion:
Based purely on the exact scenario imagined without applying it broadly across the Hobby, I would say that the only way to own a Harley Davidson bicycle is to acquire one that was originally built for Harley Davidson.
And…
Bikes can’t talk. Anything you do to a bike while you own it that changes it will probably some day be assumed by somebody to be original and there will be nobody around but the bike to explain that is not so.
At greater length:
Any bicycle that was not originally built for and sold to the Harley Davidson company, is at best a Replica or perhaps, in the case of inaccurate representations, a Tribute bike. A Dayton La France with a Harley head badge and sprocket is not a Harley Davidson bicycle and can not be changed into one. This is akin to attempting to turn one twin brother into the other. You could forge the identity and probably fool virtually everyone but true identity is a birthright. If someone builds a Harley replica for themselves, that is what they have. If that matches their aesthetic more than the original version does, I can understand the reasons for doing so but as I see it, it would take a high degree of pretend energy along with an unhealthy dose of self-delusion to actually believe the product is a Harley Davidson or to refer to it as such to oneself or others with a straight face.
Branding, and the desire to belong, drive people to spend inordinate amounts to end up with what is essentially the same product they could have at a much lower price. This is human nature and I think people can become too driven by branding and in equal parts can try too hard to avoid it. If owning a real and authenticated Harley puts one is a special circle, so does owning a fake Harley and as much as people in the second group might want to see it as one big happy circle, I’m sure most of the people in the first circle don’t
Past the issues of ownership and connoisseurship comes money. It is also easy to see that people are willing to spend a premium to own a Harley or an Indian because the cachet of the brand translates in many more circles than Dayton would. Since the true difference in the value of a Harley and a Replica Harley should lie wholly in the true provenance of the “real-deal” that distance can never be closed in replication, it would logically seem that a replica Harley should be worth no more than a La France plus the cost of a head badge and sprocket. Since the same bike is no longer original it could also be argued that, as a faux Harley, it is worth less than the original La France it was made from. Obviously cold logic often goes out the window in collector markets and the market will, with each sale, set what real and fake Harleys are worth (and what donor La Frances are worth!) Ultimately, the real mystery and general curiosity is about what premium is the going rate for a well authenticated bike and what amount people are willing to risk on questionable bikes or waste on poorly done fakes.
Down to buyers, I also find it interesting that most of the questions around trying to authenticate Harley bicycles come from novices and I think the notion of becoming knowledgeable to a degree that allows one to discern if a Harley is real or forged and the associated pay-off from finding and bringing a real Harley to market often outweigh the real core desire to own one for many would be buyers. My sense on this one is that if you have to ask, you aren’t there yet. It takes a long time and often several mistakes to get to a point that you can really trust your own opinion at the high end of the market. The fact that people are willing to pay an extreme premium for what amounts to a badge, a sprocket and assumed heritage is exactly why people fake these bikes for sale and why there is a need to be able to be confident of your own opinion that a bike is real or fake. If you can be just as happy with a LaFrance, you can save some money and be relatively sure you are not buying a fake.
As far as building replicas, the moral consequences of doing so, and the disclosure of having done so, I think like most things it is hard to know what the ultimate results of any action, good, bad or otherwise will be.
I think anything short of full disclosure at sale time regarding any bike you have is extremely poor form. While forgery for the sake of having a replica of something you like that is either purely or monetarily unattainable seems justifiable, forgery takes its pejorative connotation from the practice of incomplete disclosure to buyers for monetary gain.
If the difference between replica and forgery rests with the word and honor of the builder then where does it exist when that person is out of the picture, either after a chain of sales or through the possibility that the builder may pass on after the construction is complete but before anyone else is informed of the story.
As noted, bikes can’t talk, so no matter how well intentioned the person responsible for modification is, some day someone will likely be confused or worse duped. Hence like it or not, “Buyer Beware”, should be written at the top of every buyer’s shopping list. At the bottom of the same list should be the words “Live and Learn”