Maybe with practice it isn't difficult, but I still remember trying this for the first time. In 1985 I blew the head gasket on our '80 N/A Diesel Rabbit, and changed it myself without having the right tools to time the pump. The engine turned over by hand and with the starter motor without interference, but try as I might, I could not get the timing right and it would not start.
I took it to a mechanic recommended by a friend, but he lacked the right tools as well, and when I got it back it would only do about 40 mph (what...10 hp?). Only by taking it to a shop with the right tools would it run right.
This is not to say it can't be done, but I am a fair mechanic and couldn't get it to run when I tried it for the first time. YMMV... :wink: