Hi!
At first, sorry for my english, i'm writting from Spain and here usually english isn't well teached...
There are not many mods for Alfa 156, perhaps the most famous are the old 156 mod of Zender and some add-ons from alfisti.net or Novitec.
Zender kit:
Novitec:
And of Alfisti, you can look for some info in alfisti.net.
Regards!