You should be aware of the ghosting that is VERY obvious on some games more than others. I would be researching this FIRST and finding out if the machine you wish to do is OK with LEDs.

Some ROMs you can have the program modified and that minimises the ghosting effect but this doesn't work on ALL machines so best to start with that investigation rather than "LEDing to make it look pretty" as the first goal....

This is all going to get messy eventually as we are not going to be able to buy #47's #44's or #455 one day and instead will be forced to use LED.
Self flashing LED instead of #455??? They dont exist as far as im aware.

All my old classic woodrails with ghosting LED's and no flash in the BG...... I dont like it!