Educated SWAG...
...is all I can come up with for spring rates.
Based on wire diameter, coil count, & calibrated butt dyno.
They were aftermarket springs for other applications & cut to fit.
Approx 200/250 lb rear & 350/400 lb front.
Tho' total differential front-to-rear approx same as coilovers,
the percentage differential rear-to-front was greater.
Hence, rears were abit too soft, relative to fronts.
Traction off corners was good,
but when tire grip was upgraded,
the car started pulling wheel stands off the corners.
Like a Sprint car...