If I recall correctly, the MB12N405 would work nicely.
Main disadvantage would be it immense weight for a neo 12" driver (which defeats the original's purpose of the design).
Plans should be available in the main two topics about the PM60/90.
The MB12N405 will work but the response will need more EQ than the 351 to get it flat. If you can't find the plans send me a PM and I will send them to you - Regards Peter