Lowering block size?

[LGCC10]

I need some help! I have a 67 with coils. Putting in 2 1/2 drop spindles have a 8inch notch in the rear. Not sure what size rim and tire combo yet, if it make a difference. Will also be installing firestone bags 2600front 2500back. What size lowering block should I be using. Whould like for the truck to sit level I think. What are my options?

I put such a large notch in case I put a 4link in somewhere down the line.

Thanks,
Pete