Conversion from 6 to 8

Hello Mustang Fans!

I am planning on upgrading my engine from a straight 6 to a 302. I know that I will need to change the suspension and plan to convert the front to disk brakes. I also planning on changing the rear end to 9", any suggestions on which rear ends to use? also in changing the rear end, will that mean I will have to convert the back into disks as well? and lastly, what else will I need to change in order for my car to hold the new engine I plan to drop in( brakes, suspension, rear end, differential, etc). Your help will be much appreciated! Thanks and hope to hear from you soon!

Rod  

A good rear end ratio will be determined by how you will use the car, by what mods you do to the engine and what kind of tranny you have.
Rule of thumb:
Daily driver with auto trans and stock/mild motor for commuting/cruising go with a 2.80 or 3.00.
Street performance driver auto or stick go with 3.25/3.50 rear end.
Weekend warrior/racer go with 3.70/3.89.
If you go with an AOD tranny or 5/6 speed manual then you can try deeper gears since you will have overdrive.

In addition to the things you already mentioned you will have to change motor mounts, exhaust and radiator if you go with a 302.

If you go to a nine inch rear end you can use stock rear drums for that axle housing. You can also buy larger rear drum brakes for 9" Ford rear ends that work almost as good as discs for a lot less money. '67-72 Mustang
9 inch rear ends can be used in earlier Mustangs if you can't find a used '65/66 housing but will have to narrow it 1/2 inch on each end. If going for a daily driver commuter car you can get away with the cheaper 29 spline differential housing. For a performance car with over 300 HP try go with the 31 spline diff and axle shafts.
You will also have to get a V-8 drive shaft. The larger 9 inch rear end may cause you to have to shorten the drive shaft from an eight inch rear end car by about 1/2 inch since the 9 inch housing is bigger. If you plan to stay under 300 HP on your motor you can still use an 8 inch rear end without worrying much.
I ran a 331 *** stroker motor with about 340 horsepower through the stock 8 inch rear end in a '65 fastback with 3.25 posi gears for years with no problems....and I thrashed it too.  

You will not need to swap to disk brakes in the rear. If you can find a Lincoln Versailles the rear end is a bolt in and they came with disk brakes.  ANY 57-59 ford 9 inch rear is a bolt in, however with the spike in junk prices a year or two ago, most salvage yards cleaned out all the old stuff they had around for years!  I got $250.00 a ton for a junk vehicle a year or so ago so you can see how it would add up for them!!  As far as the suspension you will need suspension from a V-8 car.  I have a wrecked 66 V-8 car and a 3.00 posi 8 inch rear end. I know you want a 9 inch but if you are fairly stock the 8 will do just fine. you will also need a trans for a V-8.  You can e-mail me at sdully88@yahoo.com if you want to inquire about the car or have any other questions I will gladly try to help!