Why not ask Crower what springs they recommend with their cam?
I'd be very surprised if the 68404 wouldn't work for you. Sets up at near stock height, works with stock retainers and can take up to .550" lift easily though you have to watch out for retainer to seal clearance if using stock retainers.
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'72 Formula 400 Lucerne Blue, Blue Deluxe interior - My first car!
'73 Firebird 400/4-speed Black on Black, mix & match.