Should I be able to swap the driven gears for the speedos for a 2.73 rear end that was put in place of the original 3.08, without swapping drive gears? I can pull the drive and driven gears from an existing f-car with 2.73 if I need to but taking both tailshafts out may not be worth the effort for the 10% or so the speedo is off.

For confirmation that I've got the correct drive gears while I'm there, can I verify which drive gear is in the tailshaft once I pull the driven gear? Been a while since I was there.

 

do this and if everything works out then yes

 

The drive gears were the same (red) and were easily visible through the driven gear port. So no worries.

 

Just for future reference, all ratios 3.23 and numerically lower use the red, 17 tooth drive gear. It changes to the gray, 15 tooth gear for 3.42 and numerically higher gears.