Practically speaking, cleaning a filter is impractical. The filter absorbs particles, generally to about 10 microns, which become embedded into the media. Even if one could "wash" it, much of the particulates would remain embedded into the media. (The media actually filters finer as it loads up.)
In addition to a slightly smaller filter, I would suggest that you investigate whether you could find an adapter to mate the existing filter mount point on the car, to an alternate filter.
In absence of that, you could eliminate the filter in the car, and using an adapter made from an old filter, route the oil to and from an separate filter. This has been done in several applications, and I have seen someone with this arrangement on VW diesel engines.
If the engine was ever used in marine applications there may be a similar arrangement for it, allowing for a remote mount of the oil filter.
Practically, you would be well served to make friends with a fab guy.
You should also scour filter catalogs, and determine the thread pitch, diameters of the gaskets, etc. Also consider bypass pressures if your original filter as a bypass valve in it. Then I would search the catalogs looking for a similar mating thread / diameter / gasket as well as bypass pressure, and look for a filter that will fit. It might be longer, or possibly shorter. It might be listed for lawn equipment or portable power equipment.
Otherwise that fab guy's creativity will be your friend.
In the end, a 5mm smaller canister will likely have no measurable impact.
Addendum: I just saw an aux filter added to a tractor, which had used a "toilet paper filter" probably from the 1930s or 1940s. The auxiliary filter adapted to the previous filter, and allowed, in this case, a large filter, that is commonly available. I don't have a vendor and part number, but the owner said it was easy to find from their ag and fleet dealer.