Simple, if you have a stock cam and want to get a little more lift out of it, .447" stock lift becomes .465".
Perhaps you have some ported heads and a mild cam like the Comp Cams one that lifts .491" then presto, it's .513". Just remember that .520" is max lift on stock guides.
Not much, but it's a little and I think it helps. Bolt on 1.8's (not no-namers here, Harland Sharps same as Morana sells) run about $240 in a group buy. I'm sure Paul could set that up as well.
In theory roller rockers alone are supposed to help performance, but at low lift and light spring pressures it's gotta be minimal.
Just my $.02.