I have a 70 442 455. 4 speed with 391 rear gears. The tires are 255x60x15 on 8 in rims. My speedometer seems to be about 10mph slow. What combination do I need?

 

http://www.tciauto.com/tc/speedometer-gear-calculator/

Looks like a 15 drive gear and a 44 driven can you get you where you want to be.

 

Where can I buy drive and driven gears

 

https://www.ebay.com/itm/GM-GMC-TH40...kAAOSwVK9bItNE

Here you go both gears in the same auction. Depending on what you currently have you may not need to change both. If you have to change the drive gear you need to drop the driveline and pull the tail shaft, which I did without even jacking the car up in like a half hour. Also you might have to change the driven gear housing. They are only good for certain gear ranges; 34-39 or 40-45.

 

I think you miss understand this is for a manual 4 speed transmission. With 391 rear end gears.

 

Yep, I breezed right past that important detail.

 

In that case you need 8 drive gear and 23 driven. Not sure if you have 27 spline or 32 for the drive gear.

https://www.ebay.com/itm/MUNCIE-4-SP...ss!95307!US!-1

https://www.ebay.com/itm/NEW-MUNCIE-...ss!95307!US!-1

https://www.ebay.com/itm/Speedo-Driv...IAAOSw6n5XtKuG