I spent most of the afternoon finishing prepping the Muncie to go into the Chevelle, which included investigating what speedometer drive gear is in it so I can get the appropriate driven gear. To make a long story short, I cannot get the tooth count I need (19) in the size that will correctly mesh with the (1.76") drive gear.
Option 1: Remove tailhousing, remove drive gear (pressed onto shaft), press on new drive gear. This is probably the ‘right’ way to do it, but I really don’t want to pull the transmission apart and attempt to remove and install a press-fit gear on a shaft still installed in the transmission. Cost: not much; Labor: Oodles.
Option 2: Run a 22 or 23 tooth gear (the closest I can get for the drive gear I have) and run an adapter box. Cost: ~$90; Labor: Not Much
Option 3: Get a GPS-based mechanical speedometer drive I found on the internet and use that, making it irrelevant what gear set is in the transmission (and later axle ratio changes, etc). Cost: ~$350; Labor: A little more than Option 2 but nowhere near Option 1.
All this assumes that the article I read where it said the 1.76" drive gears are .531" wide, while the 1.84" are .610" is correct - I made a .53" wide piece of cardboard and stuck it in through the driven gear hole and found it to be the same width as the drive gear.