The PVB itself must be installed 12" above any water outlet that it is supplying. It should also be installed in the configuration that you see it the bell assembly needs to be able to diffuse water up and out with even distribution.
I don't have experience with blowing out system for winterization, but a lot of the talent on the site does.
Back to your question the incoming pipe to the PVB can be horizontal and 90 up and get verticle.
good luck