TromboneChat

Jj

LA Recordings would indeed have the small Olds receiver. Only late Fullerton (post ~1974) Recordings had standard small-shank receivers.
An Olds 1 mouthpiece (slightly larger than Olds 3) works better in a Recording. But it's still pretty small.
Or you could try your favorite small-shank pieces - some wobble less than others..

Native? nothing. You can reduce the diameter of any mouthpiece shank with some emery paper. I like to have the mouthpiece rotating while I do this using a drill press or lathe, but it is possible to do it without. Just work slowly -- once you go too far you can't go back. If your technical skills are lacking, any good machinist can do it. You only need to remove about 5 thousandths of an inch or so (125 microns if you are metric). Remember, this mouthpiece is now only good for an Olds special shank receiver.

I use a DE C2 in my Recording. Sometimes you can find DE stuff used. And if you wind up playing mouthpiece safari, that can quickly become much more expensive than a single DE piece.

I usually have some used parts available... If you have a pretty good idea what size you have in mind let me know.

There are also technicians who may be able to re-size the receiver to fit a modern mouthpiece. Some will net fit the receiver to a mouthpiece that you provide. I had it done to my Olds Studio trumpet. It was not prohibitively costly.