If you go completely LED bulbs for the S+ buttons and coin in, coin out, denom, and dollar bill bezel, you will need two different bulbs, the small one to replace the #68 6.3VAC and the #555 6.3VAC. I usually hone out the denom opening and put in a larger LED (the button size LED) and solder the leads to the pads. the small bulb is only bright enough to make a small circle on the 25 cent decal.
you can also replace the three fluorescent bulbs with LED strips, you will need a separate power supply to do this, I use the 5050 type strip, you can cut them to length, most have adhesive on the back of the strip. I leave the lamp in place and attach the strip directly to the lamp and secure it with zip ties run a wire from the strip to the installed power supply.
Jim