This would be my first choice if I was impatient.
-Mike

Here is a quick read of someone that already traveled the road you're on.

https://www.pinballinfo.com/community/threads/2n6427-equivalent.38846/

-Mike

None of the above.
2N6427 is a high gain NPN Darlington transistor.
MPSA13 or MPSA14 as used on Gottlieb lamp drivers are close but a bit lower in voltage rating.
Since you are driving low voltage then either of these two would work.

I have used MPSA13 and it works as Ed describes.

Two other possible solutions. I have NOT tested either of these solutions. Use at your own risk.

• Use a 2N3904 or 2N4401 but switch the TIP42 for a darlington TIP107. Instead of the high current gain in the 2N6427 driving the TIP42 the high current gain is done in the TIP107.
• Use a 2N3904 or 2N4401 but switch the TIP42 for a compatible MOSFET (IRF9530, IRF9Z34N or FQP17P06). The MOSFET is voltage driven so the high current gain of the 2N6427 is not required.

Reminder: Use at your own risk. Someone more experienced than me (like Ed) can confirm or deny the feasibility of the solutions.

MPSA12 - didn't know they actually sold those.
The MPSA12 is similar to the MPSA13 but has a lower voltage rating (20V max) and a higher current rating.
LEDs using the low lamp voltage so you should be OK but you are cutting it real close. If you use these then plan on replacing them with the right parts in the near future.

Those MPSA12's should work OK for gottlieb single lamp drivers.