Both of these games use SCRs to turn on feature lamps. SCRs and LEDs are not directly compatible. Head over the seigecraft and pick up the Bally LED adapter boards or solder resistors across every feature lamp socket.
http://www.siegecraft.us/presta/index.php?id_product=44&controller=product&id_lang=1

If you want to put LEDs in the GI. Make sure to get internally rectified LEDs or else they will be flickering 60 times a second which bugs the crap out of me.

For the feature lamps, once you have the resistors in place, you can use any LEDs in feature lamps and not worry about flickering.

Just solder 270 ohm resistors across the feature lamp lugs of LEDs that flicker. Install all the LEDs, some or most will be flickering wildly. The ones that do, put the resistor parallel across the feature lamp. You can go barrel to solder lug if that is easier.

You can also do the resistors on a separate PCB if you want a DIY project.

https://pinside.com/pinball/forum/topic/diy-led-adapter-board-for-classic-bally-or-stern-1

Sold out, next run coming soon, bench is full right now. So probably a month until I have them again.

But yes, I will be doing another run.