The season one is based from a marto ivory handle and blade, so the original prop blade can't be 76cm and have a 3cm sori, much more a 70-72cm lenght and 1,5cm sori, like any standard marto blade, if I remember correctly it also displays the original marto habaki, but has custom tsuba and additional carving on handle just like they did for the movie katana.
From season 2 there was a quite similar sword but marto provided the stunt swords, they looked identical to their mass produced highlander serie katanas, but the metal collar near dragon head was painted white, to match better the hero prop.
From season 3, they swords were the actual marto duncan, having same blade and habaki, but bronze colored collar and fuchi, and thicker tsuba (about 5,5mm thick)
I agree with the upgraded blade however, because having a real blade is much better than those awful spanish blades.
When I made my replica, I decided to carve a complete new tsuba based from the real myochin and marto together, I also carved habaki based from marto design, but sticking to the real item by different material and technic, I also carved a solid brass habaki.
To match the historical sword better, I watched the episode about the sword origin "the samurai" and replaced the marto stamp for the samurai mon, to explain why there is something carved on habaki, also, this kind of carving is historically accurate.
I also carved a real ivory handle, for a huge project, with another guy, we wanted to make the best sword ever, however the ivory piece has been lost..so were handle ferrules, lucky me, the unfinished tsuba is still here
Work visible here:
Another funny fact is they chose quite badly for their tsuba, as the myochin school was one who NEVER made soft metal tsuba, only irons were made, the rooster fight tsuba can be found from time to time, with lots of carving and design variation.