I've seen and heard about a lot of variations in the name. Modern variants are usually "Postelwait" or "Postlewait," although sometimes the "thwait" is retained.
Do you pronounce your name with an emphasis on the "Post" part? I always have. I pronounce it so it rhymes with the "Post" in "Post office" instead of with an o-sound like in "boss". A lot of people pronounce it that way and I sometimes don't correct them.
I've found a lot of people want to add an "e" to the end. I'm not sure why.
In any case, it's a name that people tend to remember once they learn it. I hope California is treating you well! My wife and I are enjoying Oklahoma. We don't make a lot of money here, but the cost of living is quite low. I'm not sure people at our stage in life could have bought a very nice house on either of the coasts.
Incidentally, my wife and I met at Oklahoma State where we were learning to be a teacher and a reporter, respectively.
The other Postelwaits that I know of are Larry and Sandy in Catoosa, Oklahoma. It's a bit of a suburb of Tulsa. Their kids (my first cousins) are Scott and Jennifer.