I installed a new Wix 46664 in my 1992 M923A2 the other day, and found a pretty simple way to do it I thought I'd share. I used some angled strut you can find and most any hardware store, and it took all of about 5 minutes to build the adapter and install the new filter. I zip tied the the strut to the existing standoffs in the removable section of the housing, I did not remove the plastic "fan" part in the forward half of the housing, as the video shows the smaller diameter of the Wix probably makes this a non-issue. I was getting a filter minder reading around 3/4 towards the "change" end of the gauge, even though my stock filter looked very clean. Now, I'm still getting a reading about 3/8ths of the way towards change, I'm not really sure what's normal on the this truck. It's definitely flowing more air by that gauge, and I think it feels like it on the butt-dyno.
I think the seal of this filter is plenty good if you take the time to make sure it's square, the length is the same and while the sealing end isn't the same design when it's forced against the flat surface it's really got no choice but to seal. Going the other way, our 939 filter in a Wix 46664 application would not work at all, the mating surfaces wouldn't line up. But since the filter seal in the fixed portion is basically just a flat plate with a hole in the middle on the 939's (at least mine is) the end of the 46664 seals against it.
Here are some pictures that should explain what I used. I cut a one foot section of the strut into four equal pieces, because I had exactly one foot on hand. That left a little room, it might take 18-24 inches of strut if you wanted to use all the available space in the housing to guide the filter. Note that the hole you see in the removed end of the can is not where the air goes or the filter seals. That is the end that pushes against the filter to seal it against the engine side.
This is pretty easy way to save 50% on air filter costs, not to mention the hassle of getting the uncommon stock filter. It flows more air that my truck seems to like, and in IMHO it's not letting any bad stuff by.