This is an interesting idea... I have plenty of thoughts.
But will they be useful thoughts?
I've done a lot of work on AutoValve harps for other people. That "trapezoidal" shaped comb presents a bunch of challenges, and I've built jigs to hold the darn thing "level" when converting them over from nails to screws. Brendan has a PowerComb that I've also tried for the AutoValve, and if you have a mouthpiece for a 10-hole Hohner or Koch chromatic kicking around, you can create an awesome improved AutoValve out of that. I've also started 3D printing replacement AutoValve combs that retain the original shape and profile but improve the chamber volumes compared to the stock comb. There's not enough room to create something as responsive as Brendan's Power Comb while retaining the trapezoidal shape... but you can certainly improve on the original comb.
Anyway, it's worth noting that the AutoValve is an Octave harmonica, so if you were to build one out of a set of chromatic plates, one reed plate would be tuned a full octave lower than the other, creating that big, full-octave effect on every hole, blow and draw. The AutoValves were also 10-hole Richter-tuned instruments. Trying to keep Richter over 12 holes is possible, but you end up with something resembling a Tremolo harmonica layout for those top 2 holes.
Another consideration is the layout of your chromatic reedplates. Many chromatics alternate between the top and bottom plate across the holes, while an AutoValve harmonica had all the low-octave reeds on the bottom and all the high-octave reeds on the top. In practice, this allows you to tilt the harmonica forward or backward to get only the low or the high reed if you want... and that would not be very clear if this direction switched every hole. There are some 12-hole harps out there where the top plate is all the "slider out" reeds, and the bottom plate is "slider in," and using this kind of harmonica might require a lot less work to set up, as you're describing.
If you're converting an older 10-hole chromatic, you may luck out and it will already be in Richter tuning, and the plates that don't alternate. But you're not going to have much luck finding two donor harps tuned an octave apart, so you'll have to do a lot of re-tuning to one plate.
The above problems could be solved if you're willing to retune all the reeds accordingly or swap them around from the top and bottom plates. An ambitious project, for sure, but possible.
If you left the reeds positioned as they are on an alternating chromatic and just used two reedplates of the same key (not an octave apart), then you'll get a Tremolo harmonica effect, rather than an octave harmonica effect, as any tiny difference between the tuning of the two plates will create that beating effect that such harps are known for.
Of course, you could also buy a Seydel Concerto Steel. This harmonica is laid out exactly like the AutoValve, with 10 holes in Richter tuning, with the lower octave on the bottom plate. The only difference is the valving, in that the upper plate is usually only half-valved, allowing you to get a lot of the same sympathetic reed bending as you'd get on a diatonic. The old AutoValve harmonicas were fully valved.
This is the Concerto Steel:
https://www.seydel1847.de/CONCERTO-STEEL/en
I sell many of them to players who have worn out their AutoValve and are looking for a replacement.
Interestingly enough, the Fanfare-S from Seydel may be precisely what you're describing... It's a Tremolo harmonica built around the body of the Seydel De Luxe Steel chromatic. The slider is removed, and just the mouthpiece remains, and the two reedplates are both tuned to the same key. If you are happy with a Tremolo effect rather than the Octave sound of an Autovalve, then this might be a great option as well.
https://www.seydel1847.de/Fanfare-S/en
Anyway, that's my thoughts on the matter. An ambitious project, to be sure!
All the best,
