Rear end gear?

[4mul8ion]

I think the 200 4R is the more common swap for the GTO as it will bolt directly to the BOP mounting pattern but maybe others have a better suggestion. In the little research I've done, you'll have to really have someone knowledgeable built one up for you to handle the power and torque. Some sources that I saw most commonly mentioned were
http://www.extremeautomatics.com/
http://www.ckperformance.com/List/20...que-Converters
http://www.jakesperformance.com/200-4R.html
http://www.cpttransmission.com/



I would go with a new housing and leave the used housings to the collectors but it's easy for me to spend your money. To answer your original ratio question, given your 5500 rpm redline and 275 35R18 tires, if you go with a 12 bolt, I'd go with a 3.31 gearset if you can find one, 3.08 otherwise. Cruise with the 3.31 and the .67 OD puts you at about 2100 RPM at 70 MPH. The 3.42 is about 2200 and the 3.08 is about 1950. If you go with a Ford 9", I'd go with a 3.25 ratio. Cruise with the 3.25 is about 2050

Just thinking about your engine again, something doesn't seem right. Are you sure about the 5200-5500 Max RPM on your 474 roller motor?