Back when I adjusted mine I used +/- .050 keepers and shims, to achieve desired spring pressures on the intake and exhaust. Gotta keep in mind distance to the valve stem seal on full open. I read .090 distance. Checkout PSI 1500 series springs. The website has a calculator for messing around with installed height to give you an example.
https://www.psisprings.com/
https://www.psisprings.com/calculate/
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68 Firebird. IA2 block, 505 cu in, E-head, Solid roller 3650 weight. Reid TH400 4:11 gear. 29" slick.
Best so far 10.12@133 mph. 1.43 60 ft.
76 Trans am, TKX .81 o/d, 3.73 Moser rearend,
468 with KRE D-ports, Doug headers, 3" Exh.
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