Kind of need a better description of how you want to mount.
On top of the parapet? On the inside of the parapet? On a non-pen sled with an extension arm that reaches up over the parapet?
If mounting to the inside wall, I'd just use two J arm feet mounted to the inside and then use a conduit bender to put two 90 degree bends into a piece of 1-1/2" conduit so that goes up and over the wall. Drill the bolt hole for the bottom foot so that the top bolt can be removed and the entire assembly can flip up inside the parapet for maintenance. You could likely get away with only one foot but I'd recommend two. If you can't bend conduit, you could use rigid 90s with couplers or have someone make the pipe for you. Likely be easier to just stop in at your electricians shop and have them bend them for you.