The optical block of the ltm version is located in the front and can be unscrewed to be used on visioflex.
Diaphragm location for 90/4 is after the second element, while in the 50/3,5 is after the first element. I dont know where is located in the M version but probably is identical to the ltm version and as E. von Hoegh wrote, they are closer to Tessar type.
I have the chromed ltm version and I like it a lot.