I had a 1987 L2550 and it had a block heater. It was located on the left side of the engine, about half way back. I'm sorry, I don't have a good picture for you as I sold the tractor. It was a great tractor, just didn't meet my needs.
It is for a B series tractor, but everything except the location of the freeze plug in the block should be the same. Good luck! Take pictures of your installation and post them. If you want, I can take a picture of the installation on my L4600.