You can certainly roll your own - they are pretty simple. As I mentioned, you want a voltage between 13.2 V and 14.4 V. Limit current for thermal reasons because the battery can handle a lot more current than a simple charger can provide when it is really flat. If you want to get fancy, remove the charge every once in awhile and measure the voltage as this will give you the state of charge, or set it up so that you provide under 2A when the battery voltage is about 12.6V, then reduces as it rises further.

The amp hour rating of your battery is not relevant to the design. and overheating is only a potential issue if you are charging a totally pancaked battery. In normal use you really don't need to worry.

The 317 is a bit light, but conceptually you could use it as a reference with a couple power transistors that turn on as required.

The circuit in the link seems fine.