I have a hard time relying on hope.
150 lbs doesn't seem like much weight but here's the thing. Throw up a 150 lb kid on the end of those horizontal brackets and tell them to start jumping around. You would be impressed by how much things move. Hour after hour and day after day little movement adds up.
Wall mount can work but give yourself every best option. Do you have the line sets already attached?
It's a lot less work to do it right at the beginning vs. fixing down the road. If you have problems it will be more than a vibrating air handler that needs fixing.
The strongest points of your vertical brackets are at the girt attachment locations. Right now the horizontal brackets are mounted well below a strong point. The free end of the vertical channel has a lot of room to flex and move.
If you want to get a better chance with hope, try putting the unit at a height where mounting point of brackets are at the girt attachment points. It would help to add isolation pads and try to keep the steel from rattling. Do the 45 degree threaded rod into the closer holes. I get the wrench thing, but man. . . Run the rod through the bottom bracket and tighten everything from easier access points.
I know it seems like a hassle to redo the mount. It's way less hassle than the options if hope doesn't work.
One big issue with steel on steel with steel fasteners is movement. Foam is a nice comfort level reinforcement. It's still not steel. If things start moving, the fastener holes start to wear, the girts are loose, tin is loose, and all of a sudden you have pieces of a building hanging around each other.