3/4 synchro issue
The scuffing you pointed out may be due to excessive endplay of the input/mainshaft. Does the tip of the input shaft look good? A failed pilot bearing could have possibly happened at some point which would have allowed the input to "wobble" around a bit and possibly cause the marks you see.
Otherwise, the snap ring that retains the syncro could be worn a bit or even failed sometime previously... Had the trans ever been apart before?




