I have just gone through this whole process and I am no Rocket Scientist but was able to get everything accomplished and am enjoying the fruits of awesome shifting.
Pelican parts has a great explanation in Tech Notes for the 914.
Installing the Coupler Bushings use a bolt with washers and a nut and pull it into position, someone on 914 World has a picture of the device they made search and find.
I used my bench vise and sockets to push the pin through, make sure you put some lithium grease on the inside of the Coupler Bushings before reinstalling the pin.
If you are struggling with replacing the Firewall Bushing, (replace this while you are in there, it is not expensive). Put the plastic piece in boiling water for three minutes, you can then push it in place with one hand.
The final thing I would suggest is make sure you put the plastic transmission cover on prior to attaching the cone screws as the plastic dot on them is for one application only, or use loctite.
You will/ should be pleasantly surprised by the results. When I started mine all I had was information gleaned from 914 World use your search option and all the answers will come to you. All in all I spent 3 hours on this and spent less than $50.00 and got 100% better and more accurate shifting. It was an extremely gratifying repair!
Vysoc