Yes, good catch on the grips being different in that scene. My suspicion is that it was required in order to rig it up to glow like it did, and they just couldn't - or didn't bother - to try and make "hollow" grips that precisely matched the normal ones. Back then, they would have had to do some special stuff to get the grips to glow so brightly, probably having a bulb that ran wires out of the gun and to a power supply someplace off camera.
Regarding the bullet, I know of a few options.
One are A-ZOOM snap-caps:
Amazon.com. These are solid anodized aluminum, and could probably be reworked and refinished as needed.
Another is these "inert" rounds from Numrich:
Dummy Ammo, .45 Colt (Long Colt). Note, that company also sells the grip screws if you felt like adding those to whatever grips you have (they could be added to the one-piece grips to make them look more authentic):
Grip Screw & Escutcheon Set, Blued-Steel, Manufactured By Colt.
Lastly, there are "fake rounds" for re-enactments such as these:
.45 revolver bullet, USA 1880 (6 units bag) (62) - Cartridges - Western and American Civil War 1861-1899 - Denix. Note, these are NOT exact replicas and will not fit in a real Colt .45 chamber.
There are actually lots of other hits for fake .45 Colt ammo... many would probably work. Most do tend to have a rough finish, though, so might take more work to match the smooth polish of the orb bullet.