If you want to build a tongue so that it won't break, here's what you do: Visualise this part at least twice as strong as it needs to be... Now double it & add some metal bits to help resist twisting, and it's just about right.

http://i181.photobucket.com/albums/x...n/cae00b09.jpg
http://i181.photobucket.com/albums/x...n/9857a76f.jpg