I think rare earth magnets would magnetise the airframe over time and could cause trouble with the compass and possibly any magnetometer that may have been installed. Of course, you could degauss the aircraft but that sounds, to me, like it's more trouble than it's worth.
The single latch on the IV has been standard from the beginning with the exception of the "Double Pin Door Latch" that was offered for a while as an option. Unlike the ones pictured in the thread, this one was mid door and was not well received. I think there are significant differences between the IV and the 7 that eliminate the need for the two pin. Primarily due to the following: The flexibility of the tubular aluminum door frame with a fiberglass or Lexan panel on the lower half - If gapping is an issue bowing the lower tube will bring both ends firmly against the exterior. There is no aluminum door seating structure requiring a precision fit and the fiberglass or Lexan covering of the lower door panel overlapping the fabric provides the seal. What Guy Buchannan did is essentially what you will find in almost every Model IV. I had the same type on my first IV - 900 hours over 9 years and on my new IV - not so many hours. Although the basic design is the same, there can be variations in the details. The following pictures are what are in my current airplane. One note: I decided that an external handle for the passenger side was not necessary because that door was seldom opened first. The passenger door only has an internal latch for opening especially for the purpose of emergency egress if necessary. Rather than having a structure that raised the pivot above the door frame, I drilled through it for the pivot - 3/16" and used half steel tubing hysoled in place to beef up the frame there a bit. My lock idea was very similar to Guy's as well.
Re: IV door latches
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