BVM use to sell a fiberglass adaptor that would attach to Dynamax or Ramtec sized inlet ducting and neck down to accomodate a Viojett fan. I'm not sure if it's still available.

Also I noticed recently that BVM now offers a spool adaptor to adapt a BVM 91 or 96 to a Rantec or Dynamax fan. I assume that this is in response to the short supply of OS 91's. That combination would work but I doubt that the BVM engines are a good match for a Dynamax or Ramtec fan.

Joe