TRW shows 2 different 455 BBB springs, both single coil with damper. I suspect the VS1020 is for the Grand Sport.
VS1016 is 295 lbs. per inch of deflection (a little less than stock), VS1020 is 373 lbs. per inch and will give high open pressure if you're not careful.
The reason there are not more interchanges is that the stovebolt springs are an odd OD, about 1.35". The more common 1.25" springs will work but you can't use the original collars.
I don't have the exact figures here...But...On a spring testing machine the 455 Buick spring was about 10 pounds more at closed pressure and 20 pounds more at .430 lift than a new stock spring.About 240 pounds actual.I spent a bit of time at the machine shop testing springs.The problem is I don't remember the part number.
The primary reason I used the Buick springs was to avoid coil bind of the stock springs.
If coil bind isn't an issue I believe with the non aggressive cams grinds used on street 235-261's,that stock springs will be ok up to about 4500 rpm.
