Saw your post at work this morning and needed to get home to measure my lenses.
My 120/6.8 has a length of 30mm and my 165/6.8 a length of 33mm (no filters of course).
The 165 is in an old Compur shutter and the 120 in a modern one. The serials are 2466854 (165) and 2530695 (120) if you want to compare the age.