Donner lens is MC ROKKOR-PF 55mm F1.7, its name plate is off.
The lens was $40 and good looking but blades were a bit sticky.
The reason to choose this lens is that it is relatively cheap and
extends 7mm to give G-Planar 35mm possibly very short MFD.

MC PF 55/1.7 > http://www.pbase.com/kkawakami/image/148895342