So Firepower or others? Are the SA3 letters critical too? I assume the DC means you need a diode?
Will any of these do the job?
AE-23-800
AE-23-800-2
SGI-23850-DC
SA3-23-900-DC
The first two coils are the same package with different diode setup.
23-850 and 23-900 are slightly less powerful but will also run slightly cooler.
I think those old machines are pretty forgiving, just if the coil is doing a lot of work it may pay to go to a 23-900 so it runs a bit cooler (with slightly less power)
If you went for 23-850 in general you would be pretty safe though.
You can use any Williams coil with the same wire gauge (23) & number of turns (800, or 850, or 900), just make sure the diode is on there and band to the positive.
