The last time I dealt with this I had a letter from the executor saying I bought the car, a copy of the POA and might have had a copy of the death certificate I can't remember now. But it was as straight forward as any normal transfer. Another time the executor signed the title and the license office had no problem confirming through their system that the person was deceased and the executor was the right person.

Of course you still need to hear from someone who's actually dealt with this in PA before