I telephoned SSPX, and I’m pretty sure the one in New Plymouth is theirs. I haven’t been able to get any information on Idaho Falls, which in any case is pretty far from Boise.
Not that I wouldn’t want to drive it, but I don’t have the money.
You are right about the New Plymouth Chapel. That is a new one to me. I might visit some time.
Heck, going to Idaho falls/American Falls from here, by the time I get to Boise it seems like I’m almost there!