What gear ratio?
 

I have a 73 mach 1 and i just ordered slicks for it, the size is 26x9.50x15, it has a four speed, i want to hit about 6000 rpms at the end of the 1/4. What gear ratio do i need?

There are alot of variables that go into gear selection. Power and red line come to mind.

Is this a built engine that can hold up to 6k?

100 mph on 26" tires in fourth gear = 4.63 gears
That's a steep gear ( I ran 4.63's on my 66 stang)

The motor is a 351c and is built, i shift @ 5500 rpms, i will use NOS 150-250, I have a hurst vgate 2 shifter just installed and is awesome. What motor and tranny did you have in the 66'. I have 3:73 detriot loc in it right know. the way the motor is built with 4 barrel heads and the cam and intake it doesnt come on till 2500 rpms. Me and my dad with thinking 4:56 gears, do we need lower?