RE: df engine and fan unit <span class=
How about running your kress fan with a [link=http://www.modelengine.com/aero/ductedfan.htm]K&B (3.5) Ducted fan engine[/link]
Or the OS 25. There's one on ebay now! do a search for "Ducted fan" there's an OS25 there!
Good luck. Let me know what you get.
Merry Christmas
Dave