How to determine gear ratio?

[sixtyfour]

I think my next big project will be re-gearing the rear axle. This will be on my 64 with 4 on the floor (1st granny gear) and a 12 bolt rear axle. Not sure what gears are in it now but I wouldn't be surprised if it had 4:11's. Motor is pretty much screaming (4000 RPM) at 75mph.

So my main question is how do I determine what gear ratio I need? I tend to drive pretty hard and fast, would like something with good acceleration on the street and good cruising speed on highway. Would I need any special tools for something like this?

Thanks
Mike