The circuit itself is very simple, as I recall: 3 leads, one to the power LED, one to the HDD LED, and a common ground. The "difficult" part is getting the right dimensions and the right LED parts that fit through the holes in the front of the case.
Here is a picture.
Thanks for that. Those LEDs are definitely an issue, and then there's the lack of resistors (which I'm guessing were probably integral). The original LEDs likely do not exist any longer, and the "height" is problematic.
If anyone can provide approximate dimensions on the LEDs, it'd be a start. Thanks!