My recommendation is to lower the rear using the hangers with the extra holes sold by companies like firm feel.

Leaf Spring Hangers
"to fit leaf springs with 20" or 22" front segments in your B-body."

From the website: These hangers are HD reproductions of the OEM hanger with the addition of an extra upper eyebolt hole so the car can be lowered 1.5 inches. The hangers are made from 0.188 steel, zinc plated for corrosion resistance and come complete with the OEM style hanger studs already pressed into place. Use the lower eyebolt hole location for stock ride height

I have news for you...
Lowering blocks are a compromise.

Going fast is dangerous and people get killed from hardware failures and bad choices. Try to make good choices.

From someone who does goes very fast doing road course 3.4 mile long hot laps for 45 minutes at time vs 1320 feet @ 10 seconds at a time.