Help me with A833 Gear ratio choice wide or close!

Stick what you got in there and run a baseline. Calculate the error in percentage. Use that percentage number to recalculate the required teeth difference.
If your Speed-O reads high, then you will have to slow the needle down, by adding teeth, and vice-versa.
Order the exact Speed-O that you need, the first time.
When rounding, I round down to run the speed-O faster than the speed-limit so's I don get no steenken Speeding teekit.

Example
suppose you stick a 34t in there and find your Speedo indicating 66mph at a true 60 mph. That is 66/60=10% high. Since it is indicating fast, you need to add teeth, 10% in this case; so 1.1x34=37.4 teeth. I round that down to 37 teeth.