Around 11 yrs ago I used a dallee electronic E unit in a 54 ballast tamper .I ordered a JV Digital Engineering Electronic unit and installed it ..
It has two 10 amp mechanical relays that work perfect its a little larger but fits as if it was made for it
All it took was @ One mm shaved off each side And solder the wires on the back of the terminals you would normally screw the wires too
The 54 body has two slots on each side that the wires will slide in to nicely..
The tamper works going forward but when reversing it does not make them move at all
Here's the link to YouTube: by typing in:
Daniels Lionel 54 Ballast tamper Version II Reverses
Or try this link: https://youtu.be/wkg5G-Zmn1s