This discussion came up in the "project games for sale" thread about what do to when a system 1 game has a dead small transformer since small transformers (B-17921) are difficult to find.
The small transformer carries a bit more than just the high voltage for the displays:
The two transformers convert the 120 volts AC input to other voltages needed for the game. [...] The small transformer outputs the main score display voltage (60/42 volts), the computer board voltage (12 volts which ultimately ends up as +5 volts), and the score display offset/reference voltages (8 and 4 volts).
It sounds like can use Boston Pinball's LED displays:
According to boston pinball, the displays do not require 69vac (60vdc & 42vdc), the offset voltages, or 5vac.
The (original) MPU requires +5vdc and -12vdc at J1.
So, it sounds like you can use an arcade power supply for the +5vdc and -12vdc, and bypass the Gottlieb power supply.
Desolder the wires for the small transformer. Put ring terminals on the hot & common wires, and connect those to the power supply. Add a ground wire from the power supply ground terminal to the EMI filter's middle terminal. Get a J1 connector (09-01-6061), and connect +5vdc and -12vdc to the appropriate pins.
3: DC GND
4: DC GND
Since it's not common to have -12vdc on arcade power supplies (but they are readily available on ATX computer power supplies), options are limited. There are -12vdc 0.5A, 1A, and 2A Mean Well power supplies available:
I'm not certain on how much draw there actually is on -12vdc.
The pinout of the 4-digit display uses +5vdc at pin 18, which is fed by the MPU (from J3) and isn't a problem.
The pinout of the 6-digit display might be problematic. It appears to take +60vdc at pin 17 from the Gottlieb power supply, and uses a 15k 1/2w resistor to drop to +5vdc. I'm not sure yet how exactly the boston pinball displays handle this. Here's two versions of the original display schematic: