Leitz equivalent lens, from about the same year, was the 3-element Elmar 90 in either M mount or LTM. A nice lens that I have used on my Canon 1Ds with various Visoflex bits.
Rico Tudor. Leica M4, IIIb, 28, 35, 50, 90, 135, 280. Contax T, RTS; Canon; Nikon; Sony; Profoto