Need help with speedo gear

I am going to be ordering some 3.73's for my cobra , and was trying to find out which speedo gear i am going to need to make it read right. I did a search on here and all I found just confused me even more.

I have a 94 cobra factory 3.08's and factory transmission. Does anybody know what speedo gear I need? I found where one post said I need a white 23 tooth, but when I look at them on yearone.com it says 21 tooth?

And does my transmission have an 8 tooth drive gear? Any help is app. as I will be ordering tonight or tomm.

So if I change the drive gear in the tranny will i still need the White 23, or will I be able to go with a lower one?

The only reason I ask is because Ive read that the white 23's dont last too long? Has anybody used the Jeep one? Does it last longer?

One more thing... say I get the gears in and the white 23 gear in , will I still need to change the drive gear in the tranny? Or will I be ok with just the white 23 gear in there? How off speedo wise do you think it would be? Sorry about all the questions, I am totally new to mustangs.