The 416 is a 15" in a 16" frame, so the WG would be nominally 15", though as I noted, the actual WG would be a bit smaller at ~12.76" to match the 416's effective piston diameter.

Yes, I imagine the m19's XO would require some tweaking.

Well, come on down and help me put my house back together and I'll be happy to re-invent the M19 if you fund the project.

Yeah, I use to recommend the Basszilla a lot, but most folks passed on it, so quit. Anyway, with various complete OB bass system designs available now it's apparently lost what little popularity it had.

GM