Here's a friendly note about LEDs...
LEDs looks absolutely spectacular in inserts, but they're pretty poor being used for GI on the playfield and under plastics. I would just do your inserts with LEDs to start and then see how you like the look of the pin. Lots of people put LEDs in for their GI and feel that the light is too harsh, too cool, or doesn't diffuse as well as the standard incandescent bulbs. After adding LEDs to around 20-30 machines, I agree that LEDs are best left to the inserts, flasher bulbs, and behind the translite.
As you're replacing bulbs, the difference between #44 and #555 is easy to spot since the #555 will be wedge-base bulbs and the #44 will be twist in/out. Most inserts will use #555, but a few could use #44. For the bulbs under your slingshots and plastics, those are almost all going to be #44s.