I have the square style lenses too. I installed these this weekend...
http://www.superbrightleds.com/specs/1156-x30.htm
I used the right angle red 1157s. The install was easy. I did have to insert the bulb and then turn the housing a bit to point to the rear. They are brighter than normal bulbs.
For $25 bucks, a cheap and useful mod. Shipping was quick too.