I went with 1.7 rollers which equal a .551 lift on my cam.... The 1.8 rollers would have put me .583 lift. So maybe the stock cam might gain about .030 of lift, maybe. I was going to do the PP dual springs with 1.8's, but now looking at going the 427 route.
Over the years increasing the rocker ratio was not a good idea for reasons mentioned above. Stock springs MAY get close to coil-bind if they float and really were not made to those spec's. Generally, take the money and do a cam with the lift and spec's you desire. The stock factory rockers are really very good parts as is. Good Luck