Im doing thisconversion at the moment but there is no way u can just bolt the front section of the 25 shaft to the 20 rear.
The 20 front shaft has the centre bearing but on the 25 the centre bearing is on the rear so its not possible. Plus the lengths are completely different.
Going to drop the shafts into a driveline shop monday and get the 25 yoke cut off and welded to the 20 shaft.
Edit: just read wax's post 3 post's up. Thats exactly what i meant