On the 261 I'm building right now the stock springs come within .060 of binding with the correct installed height at .430 lift.This is too close and spring life will be shortened.
As I mentioned elsewhere I'm using stock Buick 455 springs with a aftermarket retainer.This set up installed out of the box at 1.9 inches with 210 pounds at .430 lift.Good to about .480 lift.This will vary depending on where the valve seats are located.
