The set comes with a 3" extension. I added a 1 1/2" and a 6". (This is how my 1980 bought as new box was set up). I also added a 1/4" ratchet with 3/8" head, plus a 3/8" to 1/4" adaptor so the set can use 1/4" drive sockets.
This presented a little bit of a fitment issue, so, came up with a way to get everything in there and have the cover fully close. I store the shorty extension and adaptor in the two 3/4" sockets. The long extension and 1/4" ratchet can then fit in the ratchet chamber. Easy peazy!