The Buick 455 springs have an installed height of 1.9 and coil bind at about .510 lift.The stock 235 springs have an installed height of 1.85 and coil bind occurs at about .440.The coil bind comes off actual measurements on a properly done 235 #848 head on my recent 261 build.I used a solid lifter cam reground cam with an actual .430 lift.Any 235-261 street cam will be less than an actual .440 lift when figuring in valve lash. And actual lift taken from a mocked up engine.
The Buick springs are about 3 bucks each,
Or you can just call a major cam grinder as mentioned above.
