measure without the actual spindles, just the bracket, and the floorpan resting on the floor, that's as accurate as you could get (your floor looks rather nice and flat luckily)
1/32" shouldn't make much of a difference.. 1/16" though might already be noticable..
1/8" is a huge difference already.
Angle finder... if you have a smartphone with an accelerometer (any smartphone really) there should be an angle finder app build in or available for free in the app/play store
No, it's not the most accurate thing to get, but it's the cheapest and easiest for a very good guess
If you have a long bolt (long enough to fit through the spindle bracket and reach the floor) and a nut just stick it through the bracket and with the nut on (all the way up to the head) and undo the nut until it hits, the upper edge of the bracket while it still touches the floor.. now take it to the other side, and see if it
isn't touching the floor (bracket sits higher) not touching the nut (bracket sits lower) or touching both (bracket sits at the same height)
or straight rod and a sharpie to mark both edges of the bracket.. you get the idea
I'm sure you could still fix that, even without cracking the coat if it's not too far off.
and the handling will benefit from accuracy
'sid