I did the same mod on my Pro before I even knew about this mod. I used the short LED strips and just taped them in place across the inserts. A little scotch tape on each end of the LED strip and stuck them in place.
I made the Cross insert purple and then color matched the small cross inserts with purple bulbs. The Snake insert is orange to match the already orange snake inserts on the PF. Coffin insert is red and that matches the red coffin lock bulbs and the electric chair insert is white to match the white playfield chair inserts.
Matching the large insert colors and the small insert colors makes the end of ball tally look really nice as it shows how many crosses, chairs, etc you have. Why would the large snake insert be green when the playfield inserts are orange? Doesn't look cohesive. If you make the large cross purple, then color match the small cross inserts too and don't be halfway about it.
Also replaced the white FUEL inserts with Red-Orange-Yellow-Green and the fuel tank inserts above the large inserts also. I think doing all that really makes the playfield artwork and inserts look very cohesive.
Can probably see all that in this video I posted showing the spinners and rising cross.