Mow much tire clearance needed for leaf spring cars?

[808cuda]

Hi everyone! Newbie here!

I am building a '71 Cuda convertible and planning to fit some 335/30/18's out back.

If I am to keep the leaf spring suspension, what is the rule of thumb or recommended mininum tire sidewall-to-quarter panel and tire sidewall-to-leaf spring clearance I will need?

I have 14.5" in the wheel house width once the quarter panel lip is rolled.

the 335/30/18 mounted on a 12" wheel should have a section width of 13.5" (Michelin Pilot Sports). This gives me about 1" of room.

I was thinking 3/8" tire-to-spring and 5/8" tire-to-quarter. any thoughts?

Many thanks in advance and look forward to learning more.

Gil

P.S. I attached a pic I photochopped of hopefully the finished product.