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This is not an extreme departure from yours, but I used to use Isky # 8005-A. They have a rate of 400 lb/in.
I have used this spring for 3 years until I changed heads last Sep and needed something else for different reasons. I really liked those springs. I ran them at 140 on the seat and 380 open. The most lift I used was 0.623" gross minus 0.014" lash = 0.609" net with 1.5 rockers.
With the new heads, I ran 150 seat and 435 open on the intake and 150 seat 395 open on the exhaust. I ran a 0.650" cam with 0.028" lash up to 7500 rpm, without issue for a couple weeks (with 1.6 rockers actual net lift was 0.665"). But I now have a 0.620" cam and shift at 6500, trap at 7000. This is a net lift of 0.635" with the 1.6 rockers resulting in 425 open intake, 385 open exhaust and the same seat pressure. Time will tell.
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