If you are still interested here is a comparison I did on the TS25 76 gear box against the TM250
After a lot of actual research I can confirm
TS76 Counter shaft is the old version for TM (72)because it only has 12 teeth
1st driven gear same as 74 (29 teeth) not 75 (27 teeth)
2nd drive gear same as 74 (15 teeth)not 75(16 teeth)
2nd driven gear same as 74 (27 teeth)not 75(25 teeth)
4th drive gear same as 74 (21 teeth)not 75 (20 teeth)
5th drive gear same as 74 (23 teeth)not 75 (22 teeth)
Drive shaft is slightly different
Thrust washers are different may be because of the slightly different drive shaft
remove the neutral switch and swap washers accordingly
Primary gear on the clutch is different ?
And remove the taco drive from the oil pump
So much closer to the TM250 74 internal