What Rearend Gear ratio should I have?

[cboss70]

I have a late non-Hertz car and am wondering what rearend gears came in the car originally.  Today it appears to have 3.89 and there is no tag. I looked at the original Invoice and papers the club had, and they reference options like wheels and stripes but no optional rear things like a locker or special gears. Did the standard 66 Shelby come with 3.50 or 3.89 gears?

[s2ms]

Is this originally a 4-speed or auto trans car? 3.89's were standard on 4-speeds and 3.50's standard on autos. IIRC other ratios were optional and dealer installed.

[cboss70]

4spd car so sounds like 3.89's. Thanks.

[98SVT - was 06GT]

They all had open rear ends - even the change over cars. Detroit Lockers moved to the option column for 66.