I'm going to document the progress of rebuilding and upgrading my Avid MK-IV to FAT Avid fuselage. I hope this will make FAA inspector happy and at the same time will give prospective builders a quick look at the difference between those two airplanes. I purchased new fuselage from Steve Winder at Airdale - www.airdale.com Steve not only offers his own design but in absence of Avid Factory support - provides all parts for Avid Owners. He divides his time between native England and Idaho so the best way to contact him is via his e-mail englishav8r_at_yahoo.co.uk . FAT Avid is larger than MK-IV as a matter of fact is larger than Magnum listed below are dimensions of all three: all dimensions are in inches FAT Avid Mark-IV Magnum Across Rear door frame at the Bow 44 39 41 Across Ears (upper carry thru tube) 37.5 33.5 34.25 Across Seat Truss 40 35 36.25 Across Bottom of Panel / Knees 41.75 33 37.75 Seat Truss to Firewall 28 25 27 Toe Room (Cross Tube to Floor at Firewall) 13.25 11 13 Across Panel 38.75 29 37.5 Other things worth mentioning are: 18" longer Overall Flat firewall New door latch (cool) A bit larger doors Windshield raked back ( lower wind profile) Individually adjustable folding seats Control mixer under the seat with teleflex cables for flaperons Huge accessible in flight baggage are Larger rudder with counterbalance A few pictures: