But not all bombers have the same types of positions. Some have ventral and dorsal guns and some have turrets, se have tail guns and some don't. The B-25C and Boston/A-20 only have Top guns. The He-111 has a forward-facing dorsall gun and a rear-facing dorsal gun.
Standardized numbering by position might not work, but what about numbering from front to back?
B-17: 1 (P), 2 (NG/Bmbdr), 3 (TpT), 4 (BT), 5 (R-WG), 6 (L-WG), 7 (TlG).
Lanc: 1(P), 2 (NG/Bmbdr), 3 (TpT), 4 (TlG)