Let me use this thread to advertise my program Logic Life Search that does the same thing. In fact it doesn't just find predecessors but can also be used to prepare SAT instances for finding various other interesting patterns in cellular automata.

One of the best features is that it can treat the rules of the cellular automaton as logical variables as well as the cells of the pattern. So if you're looking for an interesting behaviour that doesn't occur in Life, LLS will find a rule where it does happen.

https://github.com/OscarCunningham/logic-life-search