It is not likely to be 5V logic.
Most transistor logic use 0 and -10 or -12.
You might first try just shorting the input
leads. This is more likely.
You might also try tracing out one flipflop
and then measure the supply voltages.
It seems there are two flops per board.
I wish I could make sense of the written lable.
I wonder what it was used for. Most counting
applications would be in decimal.