This is on the nav retrofit on the front page of this site. Notice the brackets that are on the side of the opening. These will fit in the stock location of where the 4:3 screen fits in.
You will want these part numbers to complete:
65900140347 left bracket
65900140348 right bracket
07119904046 4 x 4mm countersunk screws
I think the total price was less than $12.00. Easy to install and very secure.
Philip