Need Speedo gear for my 64 dart

OK let’s start over, I have a 21 tooth gear, the one pictured, in there already and it worked fine for the 2.76 gear I had.

I have replaced the 2.76 with a 3.55 gear, so I need at least a 27 tooth gear.

My speedo reads really high now as I expected it to with the gear change. If I put in an 18 or 19 or even 20 it will read even higher.
The gear is completely plastic with no metal parts and I have never seen one of these before. I don't think it is color coded, but if it was it looks kind of beige and certainly not grey.