I have a 1968 coupe that used to be a 6cyl, I upgraded my suspension before I dropped in a 302 but I wanted to make sure my rearend will work. I have the 5 lug wheels, I was told by some that the 5 lug means I have the 9" rearend but I can't image a 6 cyl would have that rearend in it. I thought the 5 lug meant this car just came with the bigger wheels from the factory 15s vs 14s. I talked to another guy the other day that said the 8" would be fine as long as I upgraded my axles from 28 spline to the 31. I can't find any 31 spline axles for the 8". Is there a late model rearend that would work well with my setup? I have a late model 302 and I am going to put in a T-5 or T-56 transmission.

 

If you've got the numbers that your sig indicates, I would make sure you have a 9". An 8" might be able to handle it, but I'm not sure I would risk it.

Here's some easy ways to tell a 9" and 8" apart:
http://www.kevinstang.com/Ninecase.htm

edit: Oh, now I see that you might have meant those numbers were from the 05GT you had.

 

It's most likley an 8" rear end, that will handle more HP than most people think. The 9" is kinda heavy and overkill for the majority of street cars, but on the plus side they have a ton of aftermarket support.

 

8" and 9" 5 lugs came on fords w/ 14" wheels.

I'm getting away w/ 8" on a 365HP 351W.

Really a gray area where 8" fails. Some say 300HP some say 500HP. Guess it depends on how aggressively you launch.

If you have the money go w/ 9".

If thrifting you can build an 8" dirt cheap.

Can also get a strong 8.8 cheap.

 

A lot of people seem to make the mistake of thinking if a mustang has 5 lugs that it is a 9 inch. As stated before that is not true, both 8 and 9 are 5 lug. if you have 5 lugs now chances are that it will be an 8 inch and can be bulit to handle the horse power that you are making. Since you have the axle that would be the cheap way to go. I see ads on Craig's list all the time saying they have a 65/6 with a 9 inch, they never do. It is like all the cars I have looked at that are stated to have a Boss 302. The uneducated think that since they have a 302 it must be a Boss, it never is. Your rear should handle your horse power and when you build it you can pick the gear set you want.