In general, the same mod done to a supercharged car will see a bigger overall gain.
Just as a reference from Intense'* site regarding Harland Sharp Full Roller Rocker Arms:
"The 1.80:1 Harland Sharp Full Roller Rocker Arms are a complete bolt-on kit that should increase top end power by at least 15 to 20 wheel horsepower on a supercharged vehicle and 5-10 wheel horsepower on a naturally aspirated vehicle - depending on what other modifications have been performed."

I know Fuel is not, but that quote was taken from its840 who is.

let me get this right, Smelly, you posted previously, the first half of your comment was for NA cars right? then the quote and the comment after that is for L67s right?

Also you mentioned in your first post, about eyebrows being raised, does that apply to both L36 and L67 and how high up will the eyebrow be raised?

Correct.

I have no personal experience with an L67 with 1.9s but plenty with an L36. I couldnt tell if there was any loss of low end power but the gains at upper RPMs(3500+) is VERY noticeable.

Smelbirds car did get quite a healthy gain with those rockers. Wish i could get some..