The speedometer in my 69 Chevelle is 10 mph too slow. 3:08 rear 4 speed P245 60 15 tires.
Does that require removing the tailhousing and shifter ?
How would I deterrmine the correct gear/gears ?
Thanks.

Here's a good site with all the info that you need to calculate which ones you need. I would think you may be close enough that you might only need to change the cable gear....just remember that the two have to be compatible...good luck

http://chevelleengineer.home.comcast.net/speedo.htm