Most everything is the same except the motor chamber layout. The new version is a little easier to build because it doesn't need the fill, and the chamber sizes are nearly ideal. But other than that, they are very similar horns.

Be aware that the 12π hornsub is very large and powerful. It is overkill for all but the largest rooms, theaters and outdoor use. I designed it to provide very high fidelity at high power levels, the kind of thing needed for outdoor concerts and the like. So it is probably a lot bigger than you need.