Reproducing these old truck are a good thing. With cars, people try to make "clones" all the time. Yes, some people get suckered but by people who don't know beans about the car anyway. The values of the vintage original stuff can be way up there and that drags the value of the "clones" up too. People want them and will pay. They say that out of every original muscle car, there are 2 clones. The clones are made up of original parts, or are reproduced. Heck, I have a stepside that is a clone of a Fleetside.
With the old truck market changing the way it has in the last 10 years, values will go up and people will start to clone them. The original truck values will be high, but it is the retro rod trucks that bring the best and easiest money anyway, not the restored trucks. If I were buying a resto rod truck, I don't think I would care if it had an aftermarket cab on it or not. I wouldn't blink at putting on a pickup box or tailgate from the many suppliers that reproduce them now.
For us Bolters that are getting older, having a new cab might be kind of nice instead of jerking around with all that rust floorboard and crap. They all rust in the same places anyway. How many times do I have to replace the cab corners on an old truck?
I don't care if the truck is an original or a clone. As long as the quality and beauty is there, it's a good thing. Ask Martha Stewart.