backspace question on a 66 chevelle

[sincerelyerik]

i have a 66 chevelle thats has drop spindles up from with a hotckis lowering spring and the rear has a lowering spring also im think about getting 18x8 up from and 20x10s in the back or maby 19X8 and 19X10 does anyone know how much back space i should use with the drop spindle up front?