Ok here’s what I came up with. Long story short I think it’s now 859 feet above Riverwalk with a height bump of 24 feet, give or take.
I lined up the old and new elevations so that they were roughly the same width/scale, then measured the height in Sketchup, using original elevation's height as the constant. Below is an overlay showing the possible discrepancy. I believe the Option A (height bump) one is correct, but just in case I mixed up the ground and riverwalk levels, I included a no-height-bump Option B:
