Trailer hitch drawing or plans

Dear friends: I need to install a trailer hitch on my 1989 190 D. It is to pull a small boat. Since I live in Argentina I have to make the hinch myself (actually with a friend that does this things for regular cars).
If anyone has a drawing or plans with some instructions on how is the best way to make it for the particular vehicle, I will greatly appreciate it.
thanks
Alfredo from Argentina