An old thread, but worth a follow-up.
I've converted a 1939 Carl Zeiss Jena 5cm F1.5 "T" Contax mount lens to LTM using a J-3 mount. This is one of the first coated lenses. Construction is a bit different from the earlier uncoated lenses. The Optical Fixture is made from a lighter allow than the 1938 lens that I've converted. The aperture stops down to F22 instead of F11.
VERY IMPORTANT: there is a set screw that holds the rear module in place, and another set screw that holds the front ring in place. The older lenses do not have these hidden set screws. You have to take the optics module out of the mount to see the rear set screw. Undo it to get the rear block out. You have to take off the aperture plate to get to the front ring set screw. Do not try to remove the rear block or front ring without checking for these screws. Someone tried to force the issue on the lens that I received. Some plier marks, not too bad. Beautiful Optic.