Your machine started out as a Jennings "Flat Glass" Operators bell, but was later "revamped" to add the JP front.
However, I don't think your JP front came from Rock Ola: Rock Ola made this design, they made a lot of JP fronts with many variations, but for this design, they usually embossed their name in the small black area in the center and their JP glass had horizontal and vertical bars.
Many companies produced copies of this design and replaced the Rock Ola name with their own name or just left it blank, like your machine. Below is a photo of a "no name' copy JP front to which someone added make-shift JP window bars.

- Jennings revamp