I will send you a PM with a link when I find it. The exponential horn cutoff frequency is given (I think I used 300 Hz) and the horn as is played down to 290 Hz. So if you keep the cutoff frequency, you can just make the the cells longer and it would still fit. Otherwise you would have to start from scratch. The most difficult part is the adaptor, it needed a few test prints to make it fit.
Anyone brave enough to deal with my chaotic 3D project is welcome to download it here https://drive.google.com/file/d/1gFQqIGuJ0r1W4EBtThNX68QMKK6geWf2/view?usp=sharing
I used this one https://sica.it/prodotto/cd-83-26-380/. I like plastic diaphragms or Ti with plastic surround. All Ti diaphragms were always slightly harsh - but that could be usually easily EQd out with a DSP.
I've got old plywood 1" Smith Horn back at my house - baby would aesthetically match better than multi-cell - Smith horn had some lobes - very high vertical window - great sound overall even it not considered good in these days from a technical standpoint.. Smith horn probably great for mono rig.