1935 Ford Diff Ratio Advice

[graeme_capon]

Hi,
Can someone give me some advice on working out Diff ratio, my current setup is way too low geared so im rebuilding the diff with a new crown and pinion gear set (I dont know the current diff ratio)
Some details below :
In have 1935 ford coupe ,currently building a new flathead engine for the car which will be a stroker engine 59a block
Running a 1939 Ford 3 speed
Running the standard Banjo diff
Wheel size is 15" with a set of Coker 560-15

Can someone advise of a good ratio for this setup or how to calculate what ratio is needed.

Thanks