this signal was made with a terminal that fits into the slit under the track. Should it be able to work with a traditional Lionel terminal?
Yes. But, if you are using tubular track, you should be able to use the Marx gadget with it. You just force the tabs into the gaps in the bottom of the rails. If your signal is complete, there should also be a brass strip with an insulator inside, that you press over one of the outside rails, to create a control rail. If it’s missing or you don’t like the bump that it creates, you can use an isolated rail instead. Just be sure not to connect the “lockon” gadget to that rail, since it is there to power the light.
In summary, there should be three connections, normal outside rail and center rail (the lockon) and control rail (either an isolated outside rail section or the Marx rail-cover gadget).