... Is the center white LED also a 3mm size? What kind of glue did you use to install these?
The center hole on the tender is the same size - I didn't put those in, but if you can sort the forward/reverse circuit it'd look pretty cool. On another forum I saw where someone drilled out his tender that has the molded rear lamp trim, but no existing light holes in the casting - it looked good too. I did see the same 3mm 12v LEDs in warm white, green and other colors too. I used hot glue to hold them in there because it IS possible to remove the glue - it ain't easy, but it can usually be done without busting anything - usually. Actually, if you don't clean the inside of the shell(s), the hot glue will barely stick. I like the black glue just 'cuz I reckon' it's more 'prototypical'
Black glue sticks
EDIT:
I also used the hot glue liberally (like a band-aid) inside a cracked tender shell with success - there was no fear of super-glue haze or or adhesive seeping through to spoil the remaining finish/paint.