I was pretty happy with the gascolator support bracket in the end, so I went ahead and used it.
I measured and drilled for the mounting holes in the forward tunnel, then finished riveting the tray together, primed, mounted the pumps and trial fit. It took a few goes before I got the height just right so the gascolator sample drain was protruding through the floor by the right amount.
I will probably put the filter back near the smoke oil tanks for easier access and better support for the rigid pipe.