I am fighting this same battle right now. I have 240 struts on the front, and 280's on the rear. I ordered the B30-629-Q1 gland nuts for the rears, but they are too small. I talked to John Williams in Atlanta a couple of days ago, and he remembered that he had to actually fabricate gland nuts for 280 struts in this same situation. He ended up using 280 gland nuts from Tokico and opening up the center hole to match the inside diameter of the threaded part. He then put a Bilstein gland nut on the lathe and turned it down to match the new I.D. on the Tokico gland nut, removing the threads a part of the cap portion. Finally, what remained of the Bilstein gland nut was Tig welded into the hole in the top of the Tokico gland nut. He cautioned that this had to be done extremely carefully so as not to damage the O-ring seal. He said it amounted to very quick spot welding, then cooling everything down with water or something like that.
I have not yet tried this. I am weighing this against shortening some rear strut assemblies from a 240, and bolting 280 backing plates to the hubs so I can use the dual-piston drum brake cylinders. John also said the beafier 280 stub axles will work in the 240 hubs. Does anyone know if the 280 backing plates will bolt up to 240 hubs?