There are so many variables at play here: weight of the vehicle; weight of the occupants; condition of the spring after 40+ years; personal preference of the driver; road or track biased; etc, that there isn't really a one size fits all solution to that question.
Assuming you've already taken out the three loose leaves on top of the stack, I'd suggest you try it with all the remaining leaves in place first. If it's too firm then take one of the leaves out of the next stack down. I've taken out the one from under the leaf with the 'U' clamps that hold them all together attached. It now sits where I want it without any lowering block fitted and rides compliantly allowing higher speeds to be attained with confidence on our rough old roads.
A bit of trial and error will get you there Gary.
